THE INFLUENCES OF IONIC CONCENTRATIONS AND THE INTERVALS BETWEEN CURVES ON VASCULAR TISSUE RESPONSES

Abstract

The effect of pre-exposure ("priming") of vascular smooth muscle to different levels of calcium concentrations 
before the construction of the normal concentration - response curves (CRCs) in different calcium 
concentrations, was investigated. The results showed that when the rat tail artery was primed with 3µM 
noradrenaline (NA) in 0.3mM Ca2+ or 2.5mM Ca2+ before constricting CRCs, desensitization was produced more 
quickly in the tissues primed in 2.5mM Ca2+ than the ones primed in 0.3mM. In either case, however, the 
sensitivity of the tissue later became reduced but more “stable.” This stable level is determined by the calcium 
concentration during priming and the maximum calcium concentration of the tissues’ CRC. The study 
apparently suggests that priming tissues at 0.3mM with CRC maximum at 0.3mM Ca2+ is more sitale for 
avoiding progressive desensitisation than when the tissue is primed in 2.5mM and its CRC maximum taken to 
5mM Ca2+. It follows therefore that high calcium concentration or calcium overload reduces tissues’ sensitivity. 
The effect of length of intervals between calcium concentration-response curves on the desenitisation of the rat 
tail artery was also examined. It was observed that desensitisation was not a functionof time elapsed before first 
testing, but interval between curves as well as some other factors. The progressive loss of sensitivity could 
attenuated by increasing the interval between curves. Also increasing the tissue stabilisation period beyond an 
optimal level does not confer on the tissue a greater or lesser sensitivity.