Vascular smooth muscle contractile properties in the turtle Pseudemys scripta elegans

Abstract

Abstract 1. Turtle aortic rings were characterized by high frequency spontaneous contractile activity and variable responsiveness to constrictor agents. 2. The tissue response was remarkably insensitive to temperature at a range of 37°–15°C. 3. The contractile response was effectively blocked by the calcium channel antagonist nifedipine and was substantially dependent on extracellular calcium concentrations. 4. Lowering the sodium concentration of the bath medium resulted in a strong, transient contraction followed by reduced responsiveness to norepinephrine and the absence of spontaneous activity. 5. Disruption of the vessel endothelium resulted in enhanced and reduced responsiveness to norepinephrine (NE) and acetylcholine (ACh), respectively. 6. The results indicate that the regulation of contractile function in turtle vascular smooth muscle differs in several respects from that of mammalian tissue, perhaps, reflecting the adaptation of the vasculature to low pressure and ectothermic conditions.