Effects of strontium ions on contraction and action potential in rabbit papillary muscles. A comparison with effects of tetraethylammonium ions.
The effects of Sr2+ on contraction and action potential were studied in rabbit papillary muscles and compared with effects of tetraethylammonium (TEA+). The membrane potential was measured with KCl-filled microelectrodes and the contraction was simultaneously recorded using a mechanoelectrical transducer. A partial (90%) substitution of extracellular Ca2+ (Ca2+e) by Sr2+ produced stimulation frequency-dependent prolongation of the action potential (AP) with a dominant phase "plateau" as well as prolongation of the contraction. At low frequencies where the AP prolongation was well pronounced, the contraction became biphasic. The effect of Sr2+ on both AP and contraction was blocked by nifedipine (10 mumol/l) or by increasing Ca2+e. Ryanodine suppressed the early contraction component only. AP was prolonged to a similar extent and in the same frequency-dependent manner by TEA+ (20 mmol/l). Despite similar AP configuration, no biphasic contraction developed in the presence of TEA+. High Ca2+e (10 mmol/l) or low Na+e (70 mmol/l) suppressed the TEA+ effect on AP. The data indicate that the two components of the biphasic contraction are of different origin; the early one is activated by activator cation released from the sarcoplasmic reticulum while the late one results from the Sr2+ entry across the sarcolemma via L-type Ca2+ channels.
Stengl
M
M
Department of Physiology, Faculty of Medicine, Charles University, Pilsen, Czech Republic. stengl@lfp.cuni.cz
Pucelík
P
P
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D004594:Electrophysiology; D005260:Female; D007477:Ions; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism; D010210:Papillary Muscles / Q000378:metabolism*; D011817:Rabbits; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D013324:Strontium / Q000494:pharmacology*; D019789:Tetraethylammonium / Q000494:pharmacology*
D007477:Ions; D019831:Sodium-Calcium Exchanger; D019789:Tetraethylammonium; D013324:Strontium