Differential effect of temperature on histamine- and carbachol-stimulated inositol phospholipid breakdown in slices of guinea-pig cerebral cortex

Abstract

Slices of guinea-pig cerebral cortex were incubated with [3H]-inositol at 37.degree. C before exposure to histamine or carbachol at 37.degree. C or 25.degree. C. Histamine-stimulated accumulation of [3H]-inositol 1-phosphate ([3H]-IP1) at 25.degree. C was only 5-7% of that at 37.degree. C, whereas for carbachol the response at 25.degree. C was 45-49% of that at 37.degree. C. The affinity of benzilylcholine, obtained from inhibition of carbachol-induced accumulation of [3H]-IP1 was similar at 25.degree. C and 37.degree. C, but the EC50 for carbachol was lower at 25.degree. C (20 .+-. 2 .mu.M) than at 37.degree. C (42 .+-. 2 .mu.M). The IC50 for histamine inhibition of [3H]-mepyramine binding to homogenates of guinea-pig cerebral cortex did not differ significantly at 25.degree. C and 37.degree. C. Histamine-induced accumulations of [3H]-IP2 and [3H]-IP3 at 25.degree. C, expressed as a percentage of the accumulation at 37.degree. C, were also much less than the corresponding value for carbachol. These observations imply that the locus or pathway(s) of agonist-induced formation of [3H]-IP1 are not the same for histamine and carbachol.