Large and rapid changes of myofibrillar total calcium during the cardiac cycle. Electron probe microanalysis of voltage-clamped guinea-pig ventricular myocytes.
At 36 degrees C and 2 mM [Ca2+]o, single guinea-pig ventricular myocytes were voltage clamped with patch electrodes. When paired pulsing had potentiated the contraction to the maximum, the cells were shock-frozen for electron probe microanalysis (EPMA). Shock-freezing was timed at the end of diastole (-80 mV) or at different times during systole (+5 mV). The same paired-pulse protocol was applied to another group of myocytes from which contraction was recorded and [Ca2+]i was estimated by microfluospectroscopy (50 microMNa-Indo-1). In potentiated cells, during the first pulse, contraction peaked within 128 +/- 25 ms after start of depolarization. [Ca2+]i peaked within 25 ms to 890 /+- 220 nM (mean +/- SEM) and fell within 100 ms to about 450 nM. sigma Camyo, the total calcium concentration in the overlapping myofilaments (A-band), was measured by EPMA in 17 potentiated myocytes. During diastole, sigma Camyo was 2.6 +/- 0.4 mmol/kg dry weight (dw), which can be converted to 0.65 mM (mmoles per liter myofibrillar space). Since [Ca2+]i was 180 nM, we estimate that 99.97% of total calcium is bound. A time-course for systolic sigma Camyo was determined by shock-freezing 13 cells at different times after start of depolarization to +5 mV. sigma Camyo was 5.5 +/- 0.3 mmol/kg dw (1.4 mM) after 15-25 ms, 4.6 +/- 0.5 mmol/kg dw (1.1 mM) after 30-45 ms, and 3.1 mmol/kg dw (0.8 mM) after 60-120 ms. The fast time-course of sigma Camyo suggests that calcium binds to and unbinds from troponin C at a fast rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Wendt-Gallitelli
M F
MF
Physiologisches Institut II, University of Tübingen, FRG.
Isenberg
G
G
Voigt
T
T
Ross
C
C
D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D003971:Diastole / Q000502:physiology; D004577:Electron Probe Microanalysis; D004594:Electrophysiology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000737:chemistry / Q000378:metabolism*; D009200:Myocardial Contraction / Q000502:physiology*; D009210:Myofibrils / Q000737:chemistry / Q000378:metabolism*; D013599:Systole / Q000502:physiology
D002118:Calcium