inositol 1,4,5-trisphosphate; GTPrS, guanosine 5'-3-0-(thio) The abbreviations used are: SR, sarcoplasmic reticulum; InsP3, triphosphate; PIPES, piperazine-N,N'-bis(2-ethanesulfonic acid); HEPES, N-2-hydroxyethylpiperazine-N"2-ethanesulfonic acid; FCCP, carbonyl cyanidep-trifluoromethoxyphenylhydrazone; EGTA, [ethylene his(oxyethylenenitri1o)tetraacetic acid; MPA, main pulmonary artery; MOPS, 3-(N-morpholino