Vascular smooth muscle tone is enhanced when RhoA activates Rho kinase, which phosphorylates the regulatory subunit of myosin light chain phosphatase and inhibits it. The net result of this pathway is:

• A Increased calcium influx through L-type channels
• B Accelerated calcium reuptake into the sarcoplasmic reticulum
• C Prolonged myosin light chain phosphorylation and contraction at unchanged cytosolic calcium ✓
• D Dephosphorylation of calmodulin with loss of MLCK activity

Explanation

By inhibiting myosin light chain phosphatase, Rho kinase keeps MLC20 in its phosphorylated state even after cytosolic calcium falls back toward baseline. This calcium sensitisation raises force for any given calcium level and underlies sustained vasospasm; fasudil, a ROCK inhibitor, is used clinically for cerebral vasospasm on this basis. The pathway acts downstream of calcium handling, so channel flux and SERCA activity are not changed by it.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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