TY - JOUR
T1 - Early transient depletion of extracellular Ca during individual cardiac muscle contractions.
AU - Bers, Donald M
PY - 1983/3
Y1 - 1983/3
N2 - Extracellular free [Ca] in rabbit papillary muscles was monitored using double-barreled Ca microelectrodes. These electrodes had tip diameters of 4-12 microns, electrical time constants of 2-5 ms, and electrochemical time constants of less than 30 ms. During individual beats a transient depletion of extracellular Ca (CaO) was recorded. This decrease of [Ca]O begins very early during the action potential, before significant tension development, and reaches a maximum much before the peak of developed tension (T). The depletion of CaO is blocked by CoCl2 or verapamil and enhanced by 10(-8) M isoproterenol or reduction of extracellular Na concentration to 35 mM. The magnitude of this early depletion of CaO increases in parallel with tension as a function of [Ca]O (8.46 +/- 0.98 microM at 0.2 mM CaO, 16.9 +/- 1.6 microM at 0.5 mM CaO, and 44.7 +/- 3.7 microM at 2.0 mM CaO). However the magnitude (in mV) of the recorded signal decreases with increasing [Ca]O and T, suggestive of saturation. The magnitude of this early transient CaO depletion also increases in parallel with the increase of T produced by initiating stimulation from rest (except for the first beat, which may be more dependent on stored Ca). It is probable that the depletions recorded represent Ca influx into cardiac cells from the extracellular space. The magnitude of Ca influx represented by the CaO depletions is difficult to quantitate but may be roughly in the range of Ca entry that would be required for direct activation of the myofilaments.
AB - Extracellular free [Ca] in rabbit papillary muscles was monitored using double-barreled Ca microelectrodes. These electrodes had tip diameters of 4-12 microns, electrical time constants of 2-5 ms, and electrochemical time constants of less than 30 ms. During individual beats a transient depletion of extracellular Ca (CaO) was recorded. This decrease of [Ca]O begins very early during the action potential, before significant tension development, and reaches a maximum much before the peak of developed tension (T). The depletion of CaO is blocked by CoCl2 or verapamil and enhanced by 10(-8) M isoproterenol or reduction of extracellular Na concentration to 35 mM. The magnitude of this early depletion of CaO increases in parallel with tension as a function of [Ca]O (8.46 +/- 0.98 microM at 0.2 mM CaO, 16.9 +/- 1.6 microM at 0.5 mM CaO, and 44.7 +/- 3.7 microM at 2.0 mM CaO). However the magnitude (in mV) of the recorded signal decreases with increasing [Ca]O and T, suggestive of saturation. The magnitude of this early transient CaO depletion also increases in parallel with the increase of T produced by initiating stimulation from rest (except for the first beat, which may be more dependent on stored Ca). It is probable that the depletions recorded represent Ca influx into cardiac cells from the extracellular space. The magnitude of Ca influx represented by the CaO depletions is difficult to quantitate but may be roughly in the range of Ca entry that would be required for direct activation of the myofilaments.
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M3 - Article
C2 - 6829789
AN - SCOPUS:0020729679
VL - 244
JO - American Journal of Physiology - Renal Fluid and Electrolyte Physiology
JF - American Journal of Physiology - Renal Fluid and Electrolyte Physiology
SN - 1931-857X
IS - 3
ER -