Intracellular Ca2+ transients induced by high external K+ and tetracaine in cultured rat myotubes.
Cultured myotubes from rat neonatal skeletal muscle were used to measure intracellular Ca2+ concentration ([Ca2+]i) and membrane potentials (Vm) using the Indo-1 microfluorimetry method and the nystatin perforated membrane patch technique, respectively. Sudden increases in external [K+]o from 5 mM to either 22, 42 or 84 mM elicited transient elevations in [Ca2+]i from a resting level of 106.2 +/- 10.3 nM (n = 41) to peak values of 297, 409 and 454 nM, respectively. Vm changes induced by elevated [K+]o followed the Nernst equation for [K+]o. The complex Ca2+ release response induced by elevated [K+]o can be described by a minimal model involving two components with different kinetics. This analysis revealed that the extent of the Ca2+ release by the fast component bears a sigmoidal relationship with Vm (midpoint at -47.5 mV and an effective valence of 4). Furthermore, while the fast transitory component was rather insensitive to [Ca2+]o and nifedipine, the slow component was profoundly inhibited by the dihydropyridine (10 microM) both in normal and in a Ca2+ deficient medium. Tetracaine (0.05 to 2 mM), a blocker of the charge movement associated with excitation-contraction (E-C) coupling, elicited a fast elevation in [Ca2+]i followed by a rise at a constant rate to levels as high as 1-2 microM, and the changes in [Ca2+]i were readily reversible. Simultaneous measurements of Vm and [Ca2+]i suggest that the fast component is coupled to the rapid depolarization of the membrane induced by the anesthetic. We concluded that tetracaine triggers the release of Ca2+ from internal stores by at least two different mechanisms, one of which is associated with the depolarizing effects of the drug.
Jaimovich
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Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda.
Rojas
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology*; D051381:Rats; D013748:Tetracaine / Q000494:pharmacology*
D013748:Tetracaine; D011343:Procaine; D009543:Nifedipine; D011188:Potassium; D002118:Calcium