histamine-H,-receptor-stimulated inositol phospholipid hydrolysis and calcium mobilization in the smooth-muscle cell line DDT1MF-2

The effects of raising cyclic AMP levels, by forskolin stimulation, ,f-adrenoceptor activation or cyclic AMP phosphodiesterase inhibition, on inositol phospholipid hydrolysis and increases in intracellular free [Ca2+] ([Ca2+]i) elicited by a range of agonists have been investigated in the hamster vas deferens smoothmuscle cell line DDT1MF-2. Isoprenaline {log [EC50 (M)] = -7.7+ 0.2}, forskolin and the type IV cyclic AMP phosphodiesterase inhibitor rolipram elicited significant increases in the accumulation of cyclic [3H]AMP. Pretreatment with forskolin (10 uM) attenuated histamine (100 ,M)and N6-cyclopentyladenosine (CPA; 300 nM)-induced release of intracellular Ca2 , observed when cells are stimulated in Ca2+-free buffer containing 0.1 mM EGTA. Forskolin had no effect on ATP (100 1tM)or bradykinin (1 ,uM)-stimulated release of intracellular Ca2+. Histamine-induced intracellular Ca2+ release was also inhibited by pretreatment with rolipram (100 ,uM) or the membrane-permeant