Dihydropyridine receptors are primarily functional L-type calcium channels in rabbit ventricular myocytes

W. Y W Lew, L. V. Hryshko, Donald M Bers

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Abstract

We measured [3H]PN200-110 binding and patch-clamp currents in rabbit ventricular myocytes to determine if there is a disparity between the density of dihydropyridine-specific receptors and functional L-type calcium channels, as has been reported for skeletal muscle. The dihydropyridine receptor density was 74.7±4.2 fmol/mg protein (mean±SEM, K(d)=1.73±0.29 nM, n=6) in ventricular homogenates and 147±6 fmol/mg protein (K(d)=1.15±0.16 nM, n=4) in myocytes. Ventricular homogenates contained 121±9 mg protein/g wet wt (n=7). These values were used to calculate a dihydropyridine receptor density of 12.9 dihydropyridine sites/μm2 for ventricular homogenates and 14.8 dihydropyridine sites/μm2 for myocytes. The number of functional L-type calcium channels (N) was calculated from measurements of whole-cell current (I), single-channel current (i), and open probability (p(o)), where N=I/(ixp(o)). We measured sodium current through calcium channels (I(ns)) to avoid calcium-induced inactivation. Whole-cell (I(ns)) and single-channel (i(ns) and p(o)) measurements were obtained under similar ionic conditions at a test potential of -20 mV. In six cells, the peak I(ns) was ~105 pA/pF. The single-channel conductance was 40.8 ± 2.6 pS (n=12), and i(ns) at -20 mV was 1.96 pA. The mean p(o) at -20 mV was 0.030±0.002 in 16 patches in which only a single channel was evident. The calculated density of functional L-type calcium channels was ~18 channels/μm2. Thus, in rabbit cardiac muscle, the number of L-type calcium channels (18 channels/μm2) is of similar magnitude to the density of specific dihydropyridine receptors (13-15 dihydropyridine sites/μm2). We conclude that the majority of dihydropyridine receptors in cardiac muscle are functional L-type calcium channels. For reasons discussed, this conclusion may also be valid for skeletal muscle.

Original languageEnglish (US)
Pages (from-to)1139-1145
Number of pages7
JournalCirculation Research
Volume69
Issue number4
StatePublished - 1991

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L-Type Calcium Channels
Muscle Cells
Rabbits
Myocardium
Skeletal Muscle
Calcium Channels
Sodium
Calcium

Keywords

  • Calcium channels
  • Cardiac myocytes
  • Dihydropyridine receptors
  • Excitation-contraction coupling

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine

Cite this

Dihydropyridine receptors are primarily functional L-type calcium channels in rabbit ventricular myocytes. / Lew, W. Y W; Hryshko, L. V.; Bers, Donald M.

In: Circulation Research, Vol. 69, No. 4, 1991, p. 1139-1145.

Research output: Contribution to journalArticle

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N2 - We measured [3H]PN200-110 binding and patch-clamp currents in rabbit ventricular myocytes to determine if there is a disparity between the density of dihydropyridine-specific receptors and functional L-type calcium channels, as has been reported for skeletal muscle. The dihydropyridine receptor density was 74.7±4.2 fmol/mg protein (mean±SEM, K(d)=1.73±0.29 nM, n=6) in ventricular homogenates and 147±6 fmol/mg protein (K(d)=1.15±0.16 nM, n=4) in myocytes. Ventricular homogenates contained 121±9 mg protein/g wet wt (n=7). These values were used to calculate a dihydropyridine receptor density of 12.9 dihydropyridine sites/μm2 for ventricular homogenates and 14.8 dihydropyridine sites/μm2 for myocytes. The number of functional L-type calcium channels (N) was calculated from measurements of whole-cell current (I), single-channel current (i), and open probability (p(o)), where N=I/(ixp(o)). We measured sodium current through calcium channels (I(ns)) to avoid calcium-induced inactivation. Whole-cell (I(ns)) and single-channel (i(ns) and p(o)) measurements were obtained under similar ionic conditions at a test potential of -20 mV. In six cells, the peak I(ns) was ~105 pA/pF. The single-channel conductance was 40.8 ± 2.6 pS (n=12), and i(ns) at -20 mV was 1.96 pA. The mean p(o) at -20 mV was 0.030±0.002 in 16 patches in which only a single channel was evident. The calculated density of functional L-type calcium channels was ~18 channels/μm2. Thus, in rabbit cardiac muscle, the number of L-type calcium channels (18 channels/μm2) is of similar magnitude to the density of specific dihydropyridine receptors (13-15 dihydropyridine sites/μm2). We conclude that the majority of dihydropyridine receptors in cardiac muscle are functional L-type calcium channels. For reasons discussed, this conclusion may also be valid for skeletal muscle.

AB - We measured [3H]PN200-110 binding and patch-clamp currents in rabbit ventricular myocytes to determine if there is a disparity between the density of dihydropyridine-specific receptors and functional L-type calcium channels, as has been reported for skeletal muscle. The dihydropyridine receptor density was 74.7±4.2 fmol/mg protein (mean±SEM, K(d)=1.73±0.29 nM, n=6) in ventricular homogenates and 147±6 fmol/mg protein (K(d)=1.15±0.16 nM, n=4) in myocytes. Ventricular homogenates contained 121±9 mg protein/g wet wt (n=7). These values were used to calculate a dihydropyridine receptor density of 12.9 dihydropyridine sites/μm2 for ventricular homogenates and 14.8 dihydropyridine sites/μm2 for myocytes. The number of functional L-type calcium channels (N) was calculated from measurements of whole-cell current (I), single-channel current (i), and open probability (p(o)), where N=I/(ixp(o)). We measured sodium current through calcium channels (I(ns)) to avoid calcium-induced inactivation. Whole-cell (I(ns)) and single-channel (i(ns) and p(o)) measurements were obtained under similar ionic conditions at a test potential of -20 mV. In six cells, the peak I(ns) was ~105 pA/pF. The single-channel conductance was 40.8 ± 2.6 pS (n=12), and i(ns) at -20 mV was 1.96 pA. The mean p(o) at -20 mV was 0.030±0.002 in 16 patches in which only a single channel was evident. The calculated density of functional L-type calcium channels was ~18 channels/μm2. Thus, in rabbit cardiac muscle, the number of L-type calcium channels (18 channels/μm2) is of similar magnitude to the density of specific dihydropyridine receptors (13-15 dihydropyridine sites/μm2). We conclude that the majority of dihydropyridine receptors in cardiac muscle are functional L-type calcium channels. For reasons discussed, this conclusion may also be valid for skeletal muscle.

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KW - Cardiac myocytes

KW - Dihydropyridine receptors

KW - Excitation-contraction coupling

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