The regulation of intracellular Ca2+ signals in smooth muscle cells and arterial diameter by intravascular pressure was investigated in rat cerebral arteries (∼150 μm) using a laser scanning confocal microscope and the fluorescent Ca2+ indicator fluo 3. Elevation of pressure from 10 to 60 mmHg increased Ca2+spark frequency 2.6-fold, Ca2+ wave frequency 1.9-fold, and global intracellular Ca2+ concentration ([Ca2+]i) 1.4-fold in smooth muscle cells, and constricted arteries. Ryanodine (10 μM), an inhibitor of ryanodine-sensitive Ca2+ release channels, or thapsigargin (100 nM), an inhibitor of the sarcoplasmic reticulum Ca2+-ATPase, abolished sparks and waves, elevated global [Ca2+]i, and constricted pressurized (60 mmHg) arteries. Diltiazem (25 μM), a voltage-dependent Ca2+ channel (VDCC) blocker, significantly reduced sparks, waves, and global [Ca2+]i, and dilated pressurized (60 mmHg) arteries. Steady membrane depolarization elevated Ca2+ signaling similar to pressure and increased transient Ca2+-sensitive K+ channel current frequency e-fold for ∼7 mV, and these effects were prevented by VDCC blockers. Data are consistent with the hypothesis that pressure induces a steady membrane depolarization that activates VDCCs, leading to an elevation of spark frequency, wave frequency, and global [Ca2+]i. In addition, pressure induces contraction via an elevation of global [Ca2+]i, whereas the net effect of sparks and waves, which do not significantly contribute to global [Ca2+]i in arteries pressurized to between 10 and 60 mmHg, is to oppose contraction.
Two-photon imaging of endothelin-1-mediated intracellular Ca 2+ handling in smooth muscle cells of rat renal resistance arteries