Rat arterial smooth muscle devoid of ryanodine receptor function: effects on cellular Ca 2+ handling

The roles of intracellular Ca 2+ stores and ryanodine (Ry) receptors for vascular Ca 2+ homeostasis and viability were investigated in rat tail arterial segments kept in organ culture with Ry (10 – 100 μ M ) for up to 4 days. Acute exposure to Ry or the non‐deactivating ryanodine analogue C 10 ‐O eq glycyl ryanodine (10 μ M ) eliminated Ca 2+ release responses to caffeine (20 m M ) and noradrenaline (NA, 10 μ M ), whereas responses to NA, but not caffeine, gradually returned to normal within 4 days of exposure to Ry. Ry receptor protein was detected on Western blots in arteries cultured either with or without Ry. Brief Ca 2+ release events (sparks) were absent after culture with Ry, whereas Ca 2+ waves still occurred. The propagation velocity of waves was equal (∼19 μm s −1 ) in tissue cultured either with or without Ry. Inhibition of Ca 2+ accumulation into the sarcoplasmic reticulum (SR) by culture with caffeine (5 m M ), cyclopiazonic acid or thapsigargin (both 10 μ M ) decreased contractility due to Ca 2+ ‐induced cell damage. In contrast, culture with Ry did not affect contractility. Removal of Ca 2+ from the cytosol following a Ca 2+ load was retarded after Ry culture. Thapsigargin reduced the rate of Ca 2+ removal in control cultured rings, but had no effect after Ry culture. It is concluded that intracellular Ca 2+ stores recover during chronic Ry treatment, while Ry receptors remain non‐functional. Ry receptor activity is required for Ca 2+ sparks and for SR‐dependent recovery from a Ca 2+ load, but not for Ca 2+ waves or basal Ca 2+ homeostasis.British Journal of Pharmacology (2001) 132 , 1957–1966; doi: 10.1038/sj.bjp.0703986