Rhythmical contractions in pulmonary arteries of monocrotaline-induced pulmonary hypertensive rats

[Mechanotransduction and cellular response--a challenge toward development of mechano-pharmacology]

Mechanoreception and subsequent cellular/molecular mechanisms of signal transduction pathways in response to mechanical stresses, including hemodynamic factors, passive stretching, and exercise, are ubiquitous in living organisms. Of these, the cardiovascular system involving the heart and blood vessels is known to be particularly sensitive to mechanical stimuli, for example, stretching and intraluminal pressurization, which might mimic an acute and/or chronic change in blood pressure and flow, induce a variety of responses including contraction, activation of various kinases and ionic channels, production of vasoactive substances, gene expression, and phenotype changes. We have started to clarify the mechanisms underlying this basic principle in the cardiovascular system as it is now generally considered that obesity and a lack of exercise are serious risk factors for cardiovascular diseases such as hypertension, atherosclerosis, and type 2 diabetes. We further extended our research field of mechanotransduction into adipocytes, skeletal muscle cells, and pancreatic beta cells, all of which are related to the core concerns in cardiovascular disease, including the so-called metabolic syndrome. In the present article, we discuss briefly the prologue to our study of mechanotransduction and several topics in the recent progress in this interesting area. We also emphasize that it is important to recognize biomechanical factors and control them not only for improvement in our knowledge of health and disease but also for the development of new drugs.

Pharmacological evidence for a key role of voltage-gated K+ channels in the function of rat aortic smooth muscle cells

The role of voltage-dependent (I(K(v))) and large conductance Ca(2+)-activated (BK(Ca)) K(+) currents in the function of the rat aorta was investigated using specific BK(Ca) and K(V) channel inhibitors in single rat aortic myocytes (RAMs) with patch-clamp technique and in endothelium-denuded aortic rings with isometric tension measurements. The whole-cell K(+) currents were recorded in RAMs dialysed with 200 and 444 nm Ca(2+) and in perforated-patch configuration. Electrophysiological analysis demonstrated that I(K(v)) appeared at >/=-40 mV, while BK(Ca) (isolated using 1 microm paxilline) were seen positive to -20 mV in all conditions. Voltage-dependent characteristics, but not maximal conductance, of I(K(v)) was significantly altered in increased [Ca(2+)](i). Correolide (1 microm) (a K(V)1 channel blocker) did not inhibit the I(K(v)), whereas millimolar concentration of TEA (IC(50)=3.1+/-0.6 mm, n=5) and 4-aminopyridine (4-AP, IC(50)=5.9+/-1.9 mm, n=7) suppressed I(K(v)). These results and immunocytochemical analysis suggest the K(V)2.1 channel to be a molecular correlate for I(K(v)). In nonstimulated aortic rings 1-5 mm TEA and 4-AP (inhibitors of I(K(v))), but not paxilline (1 microm), caused contraction. The frequency of contractile responses to TEA and 4-AP was increased in the presence of 10 mm KCl, which itself did not significantly affect the aortic basal tone. Phenylephrine (15-40 nm) induced sustained tension with superimposed slow oscillatory contractions (termed OWs). OWs were blocked by diltiazem, ryanodine and cyclopiazonic acid, suggesting the involvement of L-type Ca(2+) channels and ryanodine-sensitive Ca(2+) stores in this process. TEA and 4-AP, but not IbTX, paxilline or correolide, increased the duration and amplitude of OWs, indicating that I(K(v)) is involved in the control of oscillatory activity. In conclusion, our findings suggest that the K(V)2.1-mediated I(K(v)), and not BK(Ca), plays an important role in the regulation of the excitability and contractility of rat aorta.