Hypertonic and isotonic potassium solutions have different effects on vessel contractility resulting in differences in optimal resting tension in rat aorta

Aim: To compare high K⁺-induced contraction and optimal resting tension measured by two commonly used techniques of hypertonic and isotonic K⁺ in aortas with and without adventitial fat from various age rats.
Methods: Three age groups of rats (15, 25, and 62 weeks) were used to prepare thoracic aortic rings in which adventitial fat was either removed or left intact. High K⁺ (30 mmol/L)-induced contractions were observed under increasing resting tensions of 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 g. Optimal resting tension was the resting tension at which the aorta showed a maximal contraction.
Results: The contractions induced by 2 kinds of high K⁺ were significantly different. Hypertonic and isotonic K⁺ induced a different style of contraction, and the pattern varied with different ages. At the age of 15 weeks, isotonic K⁺-induced contractions were greater than hypertonic K⁺-induced contractions. However, at the age of 62 weeks, isotonic K⁺-induced contractions were smaller than hypertonic K⁺-induced contractions. Optimal resting tensions measured by 2 kinds of high K⁺ were inconsistent. Optimal resting tensions in different kinds of aortic preparations from various age rats were almost a constant of 2 g, determined by isotonic K⁺, but a variable, determined by hypertonic K⁺. The adventitial fat could delay the development of high K⁺-induced contractions at different resting tensions, but had little effect on the maximal contractions.
Conclusion: Hypertonic and isotonic K⁺ may produce different contractions resulting in differences in optimal resting tension in rat aorta.