Rat arterial smooth muscle devoid of ryanodine receptor function: effects on cellular Ca2+ handling

Abstract

The roles of intracellular Ca²⁺ stores and ryanodine (Ry) receptors for vascular Ca²⁺ homeostasis and viability were investigated in rat tail arterial segments kept in organ culture with Ry (10 – 100 μM) for up to 4 days. Acute exposure to Ry or the non‐deactivating ryanodine analogue C₁₀‐O_eq glycyl ryanodine (10 μM) eliminated Ca²⁺ release responses to caffeine (20 mM) and noradrenaline (NA, 10 μM), 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 Ca²⁺ release events (sparks) were absent after culture with Ry, whereas Ca²⁺ waves still occurred. The propagation velocity of waves was equal (∼19 μm s⁻¹) in tissue cultured either with or without Ry. Inhibition of Ca²⁺ accumulation into the sarcoplasmic reticulum (SR) by culture with caffeine (5 mM), cyclopiazonic acid or thapsigargin (both 10 μM) decreased contractility due to Ca²⁺‐induced cell damage. In contrast, culture with Ry did not affect contractility. Removal of Ca²⁺ from the cytosol following a Ca²⁺ load was retarded after Ry culture. Thapsigargin reduced the rate of Ca²⁺ removal in control cultured rings, but had no effect after Ry culture. It is concluded that intracellular Ca²⁺ stores recover during chronic Ry treatment, while Ry receptors remain non‐functional. Ry receptor activity is required for Ca²⁺ sparks and for SR‐dependent recovery from a Ca²⁺ load, but not for Ca²⁺ waves or basal Ca²⁺ homeostasis. British Journal of Pharmacology (2001) 132, 1957–1966; doi:10.1038/sj.bjp.0703986