[Changes in calcium-dependent potassium channels of isolated smooth muscle cells of the bladder in rats with experimental diabetes].

Activation of large conductance Ca2+-dependent potassium channels (BK channels) influences repolarization of the action potential and the level of the resting potential of detrusor smooth muscle cells (SMC). Overactive bladder syndrome (OBS) is one of the complications of diabetes. Here using whole-cell patch clamp technique we show sizable reduction of depolarization-evoked BK current (lBK) and decrease in the amplitude and frequency of spontaneous transient outward currents (STOCs) in isolated SMC from detrusor of rats with streptozocin-induced diabetes compared to control animals. Under the diabetes IBK density at step depolarization to +50 mV decreased from control value of 15.0+/-0.4 pA/pF to 10.0+/-0.5 pA/pF, whereas the mean values of the STOCs' frequency and amplitude at holding potential -20 mV were reduced from 12.0+/-1.5 Hz to 2.4+/-0.6 Hz and from 0.9+/-0.1 pA/pF to 0.510.1 pA/pF, respectively. Using real time RT-PCR it was found that the expression of mRNA for the BK-channel primary pore-forming KCa1.1-subunit increases under the diabetes, whilst that for the auxiliary BKCabeta1-subunit decreases. It is concluded that the observed changes in the BK-channel currents can enhance excitability of the detrusor SMCs thereby promoting myogenic OBS. However, further studies are needed to determine how the decrease in BKCabeta1 expression under the diabetes impairs functional properties of BK channels and to establish possible changes in calcium signals that modulate channel activation.

Effect of illuminated nifedipine, a potent antioxidant, on intestinal and vascular smooth muscles.

1. The effects of nifedipine (Nif) and its illuminated nitroso product nitrosopine (NTP) were investigated on lipid peroxidation, KCl elevated smooth muscle tension, and ionic currents of single smooth muscle cells. 2. Illumination of Nif at 400-700 nm within 24-48 h changed it completely to a potent antioxidant, NTP. 3. Nif relaxed the KCl-induced contractions of guinea-pig taenia caeci and rat aorta and reduced the amplitude of the evoked inward Ca2+ current of taenia caeci cells in a concentration-dependent manner. NTP (up to 100 microM) was ineffective in this respect. Pretreatment by NTP (10 microM) did not affect the actions of Nif. 4. The evidence suggests that NTP, generated by day-light illumination from Nif, exerts antioxidant activity but is devoid of voltage-dependent Ca2+ channel (VDC) blocking property and does not interfere with the action of Nif on the smooth muscle cell membrane VDC.

[Calcium current and electromechanical coupling in the smooth muscle cells of the stomach]. / Kal'tsievyi tok i élektromekhanicheskoe sopriazhenie v gladkomyshechnykh kletkakh zheludka.

The relationship between inward current and contraction was studied with double sucrose gap technique and measurement of contraction of the small muscular bundle in circular muscle from the fundus of guinea pig stomach. In voltage-clamped circular muscle, an inward current observed during depolarizing potential step was sensitive to Cd2+ or low external Ca2+ and had two components: a transient and a steady-state ones. Inactivation of this current was both voltage-dependent and Ca-current-dependent. Transient inward current activated phasic contraction, while the steady-state current activated tonic contraction. The voltage--dependence of the steady-state inward current was estimated with the Hodgkin--Huxley equation.