Calcium current measurements in acutely isolated neonatal cardiac myocytes.
Action potentials and voltage clamp-induced ionic currents were recorded in acutely isolated neonatal rabbit cardiac myocytes using the whole-cell voltage clamp technique. Time- and voltage-dependent Ca2+ currents in neonatal myocytes were elicited by depolarizations from a holding potential of -80 mV to various clamp potentials. The maximal measured inward Ca2+ current was 206 +/- 10 pA (mean +/- SEM, n = 51). The peak current occurred at a mean membrane potential of 7.8 +/- 1.3 mV (n = 51). The Ca2+ current voltage relation was shifted 26 mV in the positive direction when the external Ca2+ concentration was increased 10-fold. Ca2+ current rundown was observed with a half-time of approximately 20 min. Cells dialyzed with solution containing the Ca2+ chelating agent, EGTA (0.04 mM), had action potential durations similar to those previously reported in papillary muscle. In contrast, a higher concentration of EGTA (14 mM) prolonged the action potential duration. Control of the cell internal ionic composition was achieved by dialysis of the cell with a time constant for Na+ ions of 1.2 to 2.6 min. Tetrodotoxin (10 microM), included in some experiments to block Ca2+ entry via Na+ channels, was shown to be more than 98% effective. These results characterize the whole-cell voltage clamp technique as applied to immature heart cells.
Wetzel
G T
GT
Department of Pediatrics, University of California, Los Angeles 90024.
Chen
F
F
Friedman
W F
WF
Klitzner
T S
TS
D000200:Action Potentials; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology
D013779:Tetrodotoxin; D012964:Sodium; D002118:Calcium