Changes in intracellular Ca2+ concentration induced by L-type Ca2+ channel current in guinea pig gastric myocytes.
We investigated the relationship between voltage-operated Ca2+ channel current and the corresponding intracellular Ca2+ concentration ([Ca2+]i) change (Ca2+ transient) in guinea pig gastric myocytes. Fluorescence microspectroscopy was combined with conventional whole cell patch-clamp technique, and fura 2 (80 microM) was added to CsCl-rich pipette solution. Step depolarization to 0 mV induced inward Ca2+ current (ICa) and concomitantly raised [Ca2+]i. Both responses were suppressed by nicardipine, an L-type Ca2+ channel blocker, and the voltage dependence of Ca2+ transient was similar to the current-voltage relation of ICa. When pulse duration was increased by up to 900 ms, peak Ca2+ transient increased and reached a steady state when stimulation was for longer. The calculated fast Ca2+ buffering capacity (B value), determined as the ratio of the time integral of ICa divided by the amplitude of Ca2+ transient, was not significantly increased after depletion of Ca2+ stores by the cyclic application of caffeine (10 mM) in the presence of ryanodine (4 microM). The addition of cyclopiazonic acid (CPA, 10 microM), a sarco(endo)plasmic reticulum Ca(2+)-ATPase inhibitor, decreased B value by approximately 20% in a reversible manner. When KCl pipette solution was used, Ca(2+)-activated K+ current [IK(Ca)] was also recorded during step depolarization. CPA sensitively suppressed the initial peak and oscillations of IK(Ca) with irregular effects on Ca2+ transients. The above results suggest that, in guinea pig gastric myocyte, Ca2+ transient is tightly coupled to ICa during depolarization, and global [Ca2+]i is not significantly affected by Ca(2+)-induced Ca2+ release from sarcoplasmic reticulum during depolarization.
Kim
S J
SJ
Department of Physiology and Biophysics, Seoul National University College of Medicine, Korea.
Ahn
S C
SC
Kim
J K
JK
Kim
Y C
YC
So
I
I
Kim
K W
KW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006168:Guinea Pigs; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009130:Muscle, Smooth / Q000502:physiology*; D009529:Nicardipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D013270:Stomach / Q000502:physiology*; D013997:Time Factors
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D007211:Indoles; D015221:Potassium Channels; D012433:Ryanodine; D009529:Nicardipine; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid