Fig. 1.

Simplified representation of a vascular smooth muscle cell in the renal afferent arteriole. Not shown are background channels, and inward- and delayed-rectifier K⁺ channels. The contractile force depends on the fraction of myosin light chains (MLC) that are phosphorylated. An increase in luminal pressure generates an influx of cations into the cytosol via pressure-activated channels. The subsequent increase in cytosolic Ca²⁺ levels enhances the formation of the MLCK.CaM.Ca₄ complex, i.e., the active form of myosin light chain kinase (MLCK). As a result, the contractile force increases. MLCP, myosin light chain phosphatase; CaM, calmodulin; PMCA, plasma membrane Ca²⁺ pump; NCX, Na⁺/Ca²⁺ exchanger; SERCA, sarco/endoplasmic Ca²⁺ pump; RyR, ryanodine receptor; IP₃R, inositol triphosphate (IP₃) receptor.