A quantitative study of the relation between intracellular pH and force in rat mesenteric vascular smooth muscle

Strips of rat mesenteric artery were loaded with carboxy-seminaphthorhodafluor (SNARF) to measure intracellular pH (pHi) and force simultaneously. pHi was altered by using weak acids and bases. Alkalinization produced an increase in force. For equal elevations of pHi a greater and faster increase of force was obtained in depolarized (high K+) than in non-depolarised preparations. Acidification produced little change in force unless the tissue was contracted (high-K+), in which case it elicited relaxation. Examination of the relationship between pHi and force in depolarized preparations showed that acidification produced a greater change in force than alkalinization. Removal of weak bases produced a transient acidification that was accompanied by a fall in force in all preparations. This was followed by a secondary contraction in depolarized preparations during the period over which pHi was acidic and being restored to resting values. Some preparations demonstrated a hysteresis in the relation between pHi and force. It is concluded that the relationship between pHi and force in mesenteric vascular smooth muscle is not constant but depends on the previous history of the preparation, and may involve differences in the interactions between H+, Ca2+ and the contractile machinery.