L- and T-type calcium currents differ in finch and rat ventricular cardiomyocytes.
We compared L-type Ca current (ICaL) and T-type Ca current (ICaT) in finch and rat myocytes, using whole-cell patch clamp techniques. Cell capacitance averaged 50 +/- 4 pF in finch (n = 25) v 145 +/- 8 pF in rat (n = 38) cells, P < 0.001. In cells bathed in 1 mM Cao at 22 degrees C, peak ICaL amplitude, during a voltage clamp step (10 mM EGTA in pipette) from -45 mV to -5 mV, averaged 10.5 +/- 0.3 pA/pF in finch v 6.9 +/- 0.6 pA/pF, P < 0.001 in rat cells. ICaL inactivation kinetics were faster in finch (4.6 +/- 0.3 ms) than in rat (13.4 +/- 1.3 ms) cells. P < 0.001. ICaT was not detectable in rat cells (2 mM bathing [Ca]); but in finch cells, a large ICaT which averaged 6.8 +/- 1.4 pA/pF was activated at -30 mV and was relatively insensitive to nitrendipine (0.1 microM). The distinctive features of ICaL and ICaT in finch cells may have a role in the ability of the finch to achieve a very rapid heart rate. They may also facilitate excitation-Ca2+ release coupling in finch ventricular cells which are devoid of T tubules and have relatively few junctions between the sarcolemma and the sarcoplasmic reticulum.
Bogdanov
K Y
KY
Laboratory of Cardiovascular Science, National Institute on Aging, National Institute of Health, Baltimore, MD 21224, USA.
Ziman
B D
BD
Spurgeon
H A
HA
Lakatta
E G
EG
D000818:Animals; D001717:Birds; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004553:Electric Conductivity; D004594:Electrophysiology; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009568:Nitrendipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D012518:Sarcomeres
D009568:Nitrendipine; D002118:Calcium