Distinct transient outward potassium current (I(to)) phenotypes and distribution of fast-inactivating potassium channel alpha subunits in ferret left ventricular myocytes

Mulugu V. Brahmajothi, Donald L. Campbell, Randall L. Rasmusson, Michael J. Morales, James Trimmer, Jeanne M. Nerbonne, Harold C. Strauss

Research output: Contribution to journalArticle

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Abstract

The biophysical characteristics and α subunits underlying calcium- independent transient outward potassium current (I(to)) phenotypes expressed in ferret left ventricular epicardial (LV epi) and endocardial (LV endo) myocytes were analyzed using patch clamp, fluorescent in situ hybridization (FISH), and immunofluorescent (IF) techniques. Two distinct I(to) phenotypes were measured (21-22°C) in the majority of LV epi and LV endo myocytes studied. The two I(to) phenotypes displayed marked differences in peak current densities, activation thresholds, inactivation characteristics, and recovery kinetics. I(to,epi) recovered rapidly [τ(rec, -70 mV) = 51 ± 3 ms] with minimal cumulative inactivation, while I(to,endo) recovered slowly [τ(rec, -70mV) = 3,002 ± 447 ms] with marked cumulative inactivation. Heteropoda toxin 2 (150 nM) blocked I(to,epi) in a voltage-dependent manner, but had no effect on I(to,endo). Parallel FISH and IF measurements conducted on isolated LV epi and LV endo myocytes demonstrated that Kv1.4, Kv4.2, and Kv4.3 α subunit expression in LV myocyte types was quite heterogenous: (a) Kv4.2 and Kv4.3 were more predominantly expressed in LV epi than LV endo myocytes, and (b) Kv1.4 was expressed in the majority of LV endo myocytes but was essentially absent in LV epi myocytes. In combination with previous measurements on recovery kinetics (Kv1.4, slow; Kv4.2/4.3, relatively rapid) and Heteropoda toxin block (Kv1.4, insensitive; Kv4.2, sensitive), our results strongly support the hypothesis that, in ferret heart, Kv4.2/Kv4.3 and Kv1.4 α subunits, respectively, are the molecular substrates underlying the I(to,epi) and I(to,endo) phenotypes. FISH and IF measurements were also conducted on ferret ventricular tissue sections. The three I(to) α subunits again showed distinct patterns of distribution: (a) Kv1.4 was localized primarily to the apical portion of the LV septum, LV endocardium, and approximate inner 75% of the LV free wall; (b) Kv4.2 was localized primarily to the right ventricular free wall, epicardial layers of the LV, and base of the heart; and (c) Kv4.3 was localized primarily to epicardial layers of the LV apex and diffusely distributed in the LV free wall and septum. Therefore, in intact ventricular tissue, a heterogeneous distribution of candidate I(to) α subunits not only exists from LV epicardium to endocardium but also from apex to base.

Original languageEnglish (US)
Pages (from-to)581-600
Number of pages20
JournalJournal of General Physiology
Volume113
Issue number4
DOIs
StatePublished - Apr 1999
Externally publishedYes

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Ferrets
Potassium Channels
Muscle Cells
Potassium
Phenotype
Fluorescence In Situ Hybridization
Endocardium
Pericardium
Calcium

Keywords

  • Cardiac repolarization
  • Kv1.4
  • Kv4.2
  • Kv4.3
  • Patch clamp

ASJC Scopus subject areas

  • Physiology

Cite this

Distinct transient outward potassium current (I(to)) phenotypes and distribution of fast-inactivating potassium channel alpha subunits in ferret left ventricular myocytes. / Brahmajothi, Mulugu V.; Campbell, Donald L.; Rasmusson, Randall L.; Morales, Michael J.; Trimmer, James; Nerbonne, Jeanne M.; Strauss, Harold C.

In: Journal of General Physiology, Vol. 113, No. 4, 04.1999, p. 581-600.

Research output: Contribution to journalArticle

Brahmajothi, Mulugu V. ; Campbell, Donald L. ; Rasmusson, Randall L. ; Morales, Michael J. ; Trimmer, James ; Nerbonne, Jeanne M. ; Strauss, Harold C. / Distinct transient outward potassium current (I(to)) phenotypes and distribution of fast-inactivating potassium channel alpha subunits in ferret left ventricular myocytes. In: Journal of General Physiology. 1999 ; Vol. 113, No. 4. pp. 581-600.
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abstract = "The biophysical characteristics and α subunits underlying calcium- independent transient outward potassium current (I(to)) phenotypes expressed in ferret left ventricular epicardial (LV epi) and endocardial (LV endo) myocytes were analyzed using patch clamp, fluorescent in situ hybridization (FISH), and immunofluorescent (IF) techniques. Two distinct I(to) phenotypes were measured (21-22°C) in the majority of LV epi and LV endo myocytes studied. The two I(to) phenotypes displayed marked differences in peak current densities, activation thresholds, inactivation characteristics, and recovery kinetics. I(to,epi) recovered rapidly [τ(rec, -70 mV) = 51 ± 3 ms] with minimal cumulative inactivation, while I(to,endo) recovered slowly [τ(rec, -70mV) = 3,002 ± 447 ms] with marked cumulative inactivation. Heteropoda toxin 2 (150 nM) blocked I(to,epi) in a voltage-dependent manner, but had no effect on I(to,endo). Parallel FISH and IF measurements conducted on isolated LV epi and LV endo myocytes demonstrated that Kv1.4, Kv4.2, and Kv4.3 α subunit expression in LV myocyte types was quite heterogenous: (a) Kv4.2 and Kv4.3 were more predominantly expressed in LV epi than LV endo myocytes, and (b) Kv1.4 was expressed in the majority of LV endo myocytes but was essentially absent in LV epi myocytes. In combination with previous measurements on recovery kinetics (Kv1.4, slow; Kv4.2/4.3, relatively rapid) and Heteropoda toxin block (Kv1.4, insensitive; Kv4.2, sensitive), our results strongly support the hypothesis that, in ferret heart, Kv4.2/Kv4.3 and Kv1.4 α subunits, respectively, are the molecular substrates underlying the I(to,epi) and I(to,endo) phenotypes. FISH and IF measurements were also conducted on ferret ventricular tissue sections. The three I(to) α subunits again showed distinct patterns of distribution: (a) Kv1.4 was localized primarily to the apical portion of the LV septum, LV endocardium, and approximate inner 75{\%} of the LV free wall; (b) Kv4.2 was localized primarily to the right ventricular free wall, epicardial layers of the LV, and base of the heart; and (c) Kv4.3 was localized primarily to epicardial layers of the LV apex and diffusely distributed in the LV free wall and septum. Therefore, in intact ventricular tissue, a heterogeneous distribution of candidate I(to) α subunits not only exists from LV epicardium to endocardium but also from apex to base.",
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T1 - Distinct transient outward potassium current (I(to)) phenotypes and distribution of fast-inactivating potassium channel alpha subunits in ferret left ventricular myocytes

AU - Brahmajothi, Mulugu V.

AU - Campbell, Donald L.

AU - Rasmusson, Randall L.

AU - Morales, Michael J.

AU - Trimmer, James

AU - Nerbonne, Jeanne M.

AU - Strauss, Harold C.

PY - 1999/4

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N2 - The biophysical characteristics and α subunits underlying calcium- independent transient outward potassium current (I(to)) phenotypes expressed in ferret left ventricular epicardial (LV epi) and endocardial (LV endo) myocytes were analyzed using patch clamp, fluorescent in situ hybridization (FISH), and immunofluorescent (IF) techniques. Two distinct I(to) phenotypes were measured (21-22°C) in the majority of LV epi and LV endo myocytes studied. The two I(to) phenotypes displayed marked differences in peak current densities, activation thresholds, inactivation characteristics, and recovery kinetics. I(to,epi) recovered rapidly [τ(rec, -70 mV) = 51 ± 3 ms] with minimal cumulative inactivation, while I(to,endo) recovered slowly [τ(rec, -70mV) = 3,002 ± 447 ms] with marked cumulative inactivation. Heteropoda toxin 2 (150 nM) blocked I(to,epi) in a voltage-dependent manner, but had no effect on I(to,endo). Parallel FISH and IF measurements conducted on isolated LV epi and LV endo myocytes demonstrated that Kv1.4, Kv4.2, and Kv4.3 α subunit expression in LV myocyte types was quite heterogenous: (a) Kv4.2 and Kv4.3 were more predominantly expressed in LV epi than LV endo myocytes, and (b) Kv1.4 was expressed in the majority of LV endo myocytes but was essentially absent in LV epi myocytes. In combination with previous measurements on recovery kinetics (Kv1.4, slow; Kv4.2/4.3, relatively rapid) and Heteropoda toxin block (Kv1.4, insensitive; Kv4.2, sensitive), our results strongly support the hypothesis that, in ferret heart, Kv4.2/Kv4.3 and Kv1.4 α subunits, respectively, are the molecular substrates underlying the I(to,epi) and I(to,endo) phenotypes. FISH and IF measurements were also conducted on ferret ventricular tissue sections. The three I(to) α subunits again showed distinct patterns of distribution: (a) Kv1.4 was localized primarily to the apical portion of the LV septum, LV endocardium, and approximate inner 75% of the LV free wall; (b) Kv4.2 was localized primarily to the right ventricular free wall, epicardial layers of the LV, and base of the heart; and (c) Kv4.3 was localized primarily to epicardial layers of the LV apex and diffusely distributed in the LV free wall and septum. Therefore, in intact ventricular tissue, a heterogeneous distribution of candidate I(to) α subunits not only exists from LV epicardium to endocardium but also from apex to base.

AB - The biophysical characteristics and α subunits underlying calcium- independent transient outward potassium current (I(to)) phenotypes expressed in ferret left ventricular epicardial (LV epi) and endocardial (LV endo) myocytes were analyzed using patch clamp, fluorescent in situ hybridization (FISH), and immunofluorescent (IF) techniques. Two distinct I(to) phenotypes were measured (21-22°C) in the majority of LV epi and LV endo myocytes studied. The two I(to) phenotypes displayed marked differences in peak current densities, activation thresholds, inactivation characteristics, and recovery kinetics. I(to,epi) recovered rapidly [τ(rec, -70 mV) = 51 ± 3 ms] with minimal cumulative inactivation, while I(to,endo) recovered slowly [τ(rec, -70mV) = 3,002 ± 447 ms] with marked cumulative inactivation. Heteropoda toxin 2 (150 nM) blocked I(to,epi) in a voltage-dependent manner, but had no effect on I(to,endo). Parallel FISH and IF measurements conducted on isolated LV epi and LV endo myocytes demonstrated that Kv1.4, Kv4.2, and Kv4.3 α subunit expression in LV myocyte types was quite heterogenous: (a) Kv4.2 and Kv4.3 were more predominantly expressed in LV epi than LV endo myocytes, and (b) Kv1.4 was expressed in the majority of LV endo myocytes but was essentially absent in LV epi myocytes. In combination with previous measurements on recovery kinetics (Kv1.4, slow; Kv4.2/4.3, relatively rapid) and Heteropoda toxin block (Kv1.4, insensitive; Kv4.2, sensitive), our results strongly support the hypothesis that, in ferret heart, Kv4.2/Kv4.3 and Kv1.4 α subunits, respectively, are the molecular substrates underlying the I(to,epi) and I(to,endo) phenotypes. FISH and IF measurements were also conducted on ferret ventricular tissue sections. The three I(to) α subunits again showed distinct patterns of distribution: (a) Kv1.4 was localized primarily to the apical portion of the LV septum, LV endocardium, and approximate inner 75% of the LV free wall; (b) Kv4.2 was localized primarily to the right ventricular free wall, epicardial layers of the LV, and base of the heart; and (c) Kv4.3 was localized primarily to epicardial layers of the LV apex and diffusely distributed in the LV free wall and septum. Therefore, in intact ventricular tissue, a heterogeneous distribution of candidate I(to) α subunits not only exists from LV epicardium to endocardium but also from apex to base.

KW - Cardiac repolarization

KW - Kv1.4

KW - Kv4.2

KW - Kv4.3

KW - Patch clamp

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