Although alterations in Ca2 +metabolism have been demonstrated in subcultured aortic myocytes of spontaneously hypertensive rats (SHR), changes in intact tissue have not been described. This study compares Ca2 +metabolism in intact mesenteric resistance arteries and in myocytes that were derived from mesenteric arteries and maintained in primary and long-term culture. Using fura-2, basal levels of Ca2 +were found to be similar in intact vessels of SHR and Wistar-Kyoto normotensive rats (WKY), and in primary and first-passage myocytes of the two strains. During subculture, basal levels of Ca2+became elevated in myocytes of SHR. When norepinephrine-induced Ca2+mobilization was examined, the threshold of resistance arteries was lower in SHR, but differences were not detected with higher concentrations of the agonist. Norepinephrine-induced Ca2+mobilization also did not differ between primary myocytes of the two strains. Angiotensin II elicited greater intracellular Ca2 +responses in myocytes of SHR at passages 1, 3 and 5. Cell growth was assessed at each passage level. While no strain differences were detected in primary, first- and second-passage cells, the growth rate became elevated in SHR in subsequent passages. These results are consistent with the hypothesis that vascular myocytes cultured from SHR with established hypertension exhibit differences in Ca2+metabolism that are not present in the intact vessel wall. Furthermore, intracellular Ca2+appears to be elevated in myocytes of SHR when the rate of proliferation is increased.