Abstract
Abstract: :
Purpose: To study the effect of normocapnic (NA) and hypercapnic acidosis (HA) on the tone, the intracellular calcium level, and the membrane potential of smooth muscle cells in porcine retinal arterioles. Methods: Twenty–four porcine retinal arterioles were mounted in a wire myograph for isometric recording of wall tension. The vessels were precontracted with 0.3 µM U46619 and exposed to both NA (pH=7.0) and HA (pH=7.0). Intracellular calcium was measured using the fluorophore Fura–2AM (n=12). In six vessels 0.1 mM NG–Nitroarginine Methyl Ester (L–NAME) was added to block NO–synthesis. The membrane potential of the smooth muscles in situ was measured with sharp glass electrodes (n=12). Results: NA and HA caused a similar significant decrease in wall tension (p<0.01), membrane potential (from –18±0.7 mV during precontraction to –26±1.9 mV in NA (p=0.002) and –24±2.6 mV in HA (p=0.02)), and similar decrease in intracellular Ca2+ (p<0.01), which was unaffected by inhibition of NO–synthesis. Conclusions: Acidosis induced relaxation of the tone in isolated porcine retinal arterioles is associated with a decrease in intracellular calcium and a hyperpolarisation of the smooth muscle cells. The acidosis induced relaxation is independent of CO2, and is not mediated through NO.
Keywords: blood supply • PH regulation/protons • electrophysiology: non–clinical