Abstract
To test the hypothesis that relations between myogenic tone and cytosolic Ca++ are enhanced by myofilament Ca++ sensitization but attenuated by high proportions of non‐contractile smooth muscle cells, in immature compared to mature rat cerebral arteries, three protocols were performed in middle cerebral arteries (MCA) from P14 and adult rats. Myofilament Ca2+ sensitivity in β‐escin permeabilized arteries increased with pressure in P14, but not adult, MCA. Cyclopiazonic acid (a release inhibitor) increased diameter and reduced Ca++ in adult MCA, but increased diameter with no change in Ca++ in the P14 MCA. La3+ (an influx inhibitor) increased diameter and decreased Ca++ in adult MCA, but in P14 MCA diameter increased without any significant decline in Ca++. With La3+ and CPA, diameter was passive in adult and P14 MCA, but Ca++ declined only in adult MCA. Colocalization between α‐actin and SM2 myosin was >2‐fold greater in adult than in pup MCA.. These data suggest that compared to adult MCA, pup MCA rely more on myofilament Ca++ sensitization and Ca++ influx to maintain myogenic reactivity. The inability of La3+ to reduce cytosolic Ca++ in the pup MCA appears due to La3+‐insensitive non‐contractile smooth muscle cells that contribute to the spatially averaged measurements of Ca++ but not contraction. Supported by USPHS grant HL54120, HD31266, and HL64867.
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