The effects of pH on the sodium-withdrawal contractures evoked from frog atrial trabeculae.
Contractures can be evoked from frog atrial trabeculae by raising extracellular pH in Na-free fluid after the spontaneous relaxatin of the tension evoked by removing extracellular Na+. These alkalinity contractures are unaffected by local anaesthetics but are absent following a brief perfusion with Ca-free fluid but are partially inhibited by local anaesthetics. Perfusion by solution containing a high Pco2 fails to induce contractures. The relationship between [Na]0 and tension is altered by changing extracellular pH; acidic fluids below pH 6.0 reduce tension and alkaline fluids increase tension over the whole range. NH4Cl has the same effect as alkaline fluids while CO2-containing fluid has no effect. These results can be interpreted if the effects of variation of extracellular pH, on Na-withdrawal contractures, are mediated by changes in intracellular pH which in turn affect the Ca-sensitivity of the contractile proteins.
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002245:Carbon Dioxide; D006325:Heart Atria; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D011343:Procaine / Q000494:pharmacology; D011894:Rana pipiens; D012964:Sodium / Q000502:physiology*; D013748:Tetracaine / Q000494:pharmacology
D000643:Ammonium Chloride; D013748:Tetracaine; D002245:Carbon Dioxide; D011343:Procaine; D012964:Sodium; D002118:Calcium