Actions of extracellular chloride ion substitution on contractility of isolated ventricular myocardium.
OBJECTIVE
Replacement of extracellular chloride ions by some other anions exerts a positive inotropic effect on isolated cardiac muscle preparations. The aim of this study was to determine whether the increase of force was mediated by an intracellular alkalosis.


METHODS
Isometric tension development was measured using guinea pig papillary muscles during replacement of superfusate Cl- with isethionate ions. Intracellular pH and L-type Ca2+ currents were measured in isolated myocytes using epifluorescence microscopy and a switch-clamp technique respectively.


RESULTS
Reduction of extracellular Cl- increased tension, a phenomenon which was partially inhibited with the anion exchange blocker SITS. Force was also increased by reducing superfusate PCO2. Reduction of superfusate [Cl-] and PCO2 both produced concentration dependent intracellular alkalosis. The relationship between the changes to tension and intracellular pH was different when either the superfusate [Cl-] or PCO2 was reduced, less pronounced when the [Cl-] was reduced. An increase of the L-type Ca2+ current was produced in low [Cl-] solutions which could be attributed to the accompanying intracellular alkalosis.


CONCLUSIONS
The positive inotropic effect of superfusate Cl- removal can only partially be explained by intracellular alkalosis. Other, as yet unknown, changes must determine the remainder of the inotropic response.
Department of Physiology, UMDS, London, United Kingdom.
C H
CH
Fry
H
H
Griffiths
S K
SK
Hall
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism*; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010210:Papillary Muscles; D010477:Perfusion
D002712:Chlorides; D002245:Carbon Dioxide; D000252:Calcium-Transporting ATPases