title: Relationship between intracellular pH and tension development in resting ventricular muscle and myocytes.
abstract: Simultaneous measurements of intracellular pH (pHi) and tension development were made in resting cat papillary muscles and resting ventricular myocytes (cat, guinea pig). pH microelectrodes and the fluorescent indicator carboxy-seminaphthorhodafluor-1 (SNARF-1) were used to measure pHi in muscles and myocytes, respectively. pHi-induced changes in isometric muscle tension and myocyte length were elicited by variations in PCO2, HCO3-, and [NH4Cl]. Increased pHi elevated resting tension and decreased resting cell length, whereas decreased pHi decreased tension and increased cell length. The tension-pHi and cell length-pHi relationships were nonlinear and displayed hysteresis. A reduction in extracellular [Ca2+] from 2.7 to 0.5 mM caused little or no change in the tension and cell length responses to elevated pHi. Ca2+ uptake and/or release by the sarcoplasmic reticulum (SR) does not appear to be involved in the tension response to intracellular alkalosis because the response was unaffected by a postpacing rest period and was not inhibited by ryanodine (5 microM), which depletes SR Ca2+ stores. The cross-bridge inhibitor 2,3-butanedione monoxime (15 mM), but not internal dialysis with 14 mM ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid, inhibited myocyte contractures elicited by elevated pHi. The latter finding suggests that factors other than pHi-induced increase in myofilament Ca2+ sensitivity may contribute to the resting contractile response to elevated pHi.
authors.affiliation: Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City 84112.
authors.forename: K W
authors.initials: KW
authors.lastname: Spitzer
authors.forename: J H
authors.initials: JH
authors.lastname: Bridge
mesh_terms: D000818:Animals; D002415:Cats; D006168:Guinea Pigs; D006352:Heart Ventricles; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology*; D012146:Rest