Preload-induced stress relaxation and membrane current changes in the denervated intact smooth muscle

Ni Zhi-zhan; Li Jie-yao; Zhang Pei; Xia Li; Ye Si-qi; Annie Christel Bel; Fan Shou-yan; Piao Ling-hua; Chen Zhi-bin; Gao Ling-feng; Wang Yang

doi:10.3969/j.issn.2095-4344.2016.24.014

Abstract：BACKGROUND:Muscle stretch test is a method for testing mechanical properties of denervated muscle under diverse loads. OBJECTIVE:To observe changes of spontaneous tension wave in myography and membrane electric current in aorta smooth muscle samples under several preload conditions. METHODS:Denervated intact smooth muscle samples were taken from the Kunming mouse aorta and urinary bladder wal. Smooth muscle samples were fixed on a micro positioning device and the first stretchwasinduced fora passive tension up to 1 g, this position was determined as the initial length (L0). Intermittently, withincreasing sample length from L0every 5 minutes, the 1stand 10thstretch were recorded as low-(L0+1) and high-preload (L0+10). 3%CaCl2and 0.05% nitrendipine were dropped on the samplesbeforeL0+1and L0+10stretch were recorded. Membrane current changes were evaluated by glass microelectrodes and MultiClamp 700B Amplifier and pClamp 10 analyzer software. The membrane currentchanges after L0+1and L0+10were analyzed. RESULTS AND CONCLUSION:Prolonged stress relaxation phase was shortened with increasing preload in smooth muscle preparations. The stress relaxation phase in smooth muscle samples from urinary bladder wal wasshorter than aorta samples. It was revealed that there were compliance differences between two kinds of smooth muscle samples. In aorta samples, myogenic spontaneous contraction amplitude during stress relaxation and membrane current were significantly increased with increasing preload. Increased amplitude and frequency of membrane current in aorta smooth muscle samples under high calcium concentration (3% CaCl2) were inhibited by L-type calcium channel blockade (0.05% nitrendipine). Colectively, increasedpreload in smooth muscle samples induced a directly decrease of compliance with an enlargement of myogenic spontaneous contraction amplitude. It appeared vital in particular in aorta samples. Membrane current significantly enhanced in spontaneous contraction period suggested the mechanical stretching ionic inward flow involved in this period. Membrane current amplitude was increased by high-preload under elevated calcium conditions; however, this change was suppressed by L-type calcium channel blockade. This study indicates quick stretching influences not only mechanicaly-gated channels in smooth muscle, but also the activation of L-type calcium channel.