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.
Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda.
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Jaimovich
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Rojas
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