MYOGENIC TONE IN JUVENILE RAT MCA IS RESISTANT TO BLOCKADE OF CALCIUM INFLUX AND RELEASE OF INTRACELLULAR CALCIUM

Abstract

We measured pressure‐evoked (20–80 mmHg) myogenic tone and wall intracellular calcium ([Ca 2+ ]i) in endothelial denuded, Fura‐2 loaded segments of middle cerebral arteries (MCA) from pup (P14) and adult (6 months) SD rats. Measurements were done in calcium replete HEPES buffer in the absence and presence of, cyclopiazonic acid (CPA, 10 μM) to deplete [Ca 2+ ]i stores or with the calcium channel blocker, lanthanum (La 3+ , 100 μM), or with La 3+ plus CPA. Myogenic tone was developed at each pressure step with corresponding increases in [Ca 2+ ]i, in adult and pup MCA. CPA reduced myogenic tone and [Ca 2+ ]i in the adult MCA, while in the pup CPA decreased myogenic tone with no change in [Ca 2+ ]i and tone remained significantly greater in the pup as compared to the adult. La 3+ decreased myogenic tone and [Ca 2+ ]i in the adult MCA and in the pup tone also declined but was greater as compared to adult without any significant decline in [Ca 2+ ]i. In the presence of La 3+ and CPA, myogenic tone was completely lost in the adult with a corresponding decline in [Ca 2+ ]i, however, in the pup MCA, myogenic tone while severely depressed, significant tone remained with no significant change in [Ca 2+ ]i. These data suggest that in juvenile cerebral arteries there appears to be a pool of [Ca 2+ ]i that maintains minimal myogenic response when influx and release of calcium are blocked. Supported in part by NIH R01 #HL69078‐01 and NIH P01 # 31226