Kochenov .V.,Ukrainian Academy of Sciences |
Kochenov .V.,Dnipropetrovsk Medical Academy of the Ministry of Public Health of Ukraine |
Poddubnaya E.P.,Dnipropetrovsk Medical Academy of the Ministry of Public Health of Ukraine |
Korogod S..,Ukrainian Academy of Sciences
Neurophysiology | Year: 2015
The work was aimed at the search for approaches to solving the problem of biophysically reasonable selection of the parameters of electrical stimulation of smooth muscle cells (SMCs) of the urinary bladder detrusor (UBD). Such stimulation is widely used in the rehabilitation of patients with surgical correction of congenital malformations accompanied by total or partial deficiency of the M2/M3 cholinergic receptors in the UBD. A computer model built on the basis of experimental data on ion channels and pumps of the sarcolemma and mechanisms of regulation of the intracellular calcium concentration ([Ca22+]i), providing both electrogenesis and the contractile function of the cell inherent to the biological prototype, was used. We studied changes in the membrane potential, partial transmembrane currents, and [Ca2+]i, caused by depolarizing current pulses applied with constant frequencies and combined in “packs” or “envelopes” typical of the protocols of rehabilitation stimulation; the stimuli had constant or trapezoid-modulated amplitudes. The examined UBD SMC responded to a single pulse by generation of the action potential (AP) close in its properties to the prototype. Stimulation by both packs and envelopes of identical pulses eventually led to the establishing of equal forced electrical and concentration oscillations with the parameters depending on the duration of interpulse intervals (IPIs). Such oscillations caused by stimulation with 5- and 50-msec-long IPIs, typical of the rehabilitation protocols and comparable with the durations of the absolute and relative refractoriness of the model SMC, significantly differed in the pattern of the regenerative responses (APs) and in the range and mean levels of depolarization shifts of the membrane potential and those of [Ca2+]i, which were greater at high-frequency stimulation. In the case of short IPIs, [Ca2+]i, having no time to return to the basal level, oscillated within a range of values which in other excitable cells are considered to exceed significantly the physiological norm. These data emphasize the necessity to estimate the exact kinetic characteristics of the mechanisms underlying the inflow and extrusion of Ca2+ in the UBD SMC necessary for a biophysically justified choice of the parameters of rehabilitation stimulation that would prevent possible cytotoxic side effects associated with excessively long-lasting high levels of [Ca2+]i. Essential for the observed processes and, therefore, requiring targeted studies, was such a parameter of UBD SMCs as the reversal potential for Ca2+-dependent chloride current (ECl); this current is activated, in particular, by parasympathetic action on the M2/M3 receptors. When high-frequency oscillations of the membrane potential periodically exceeded the ECl level, the mentioned current changed its main (depolarizing) direction to the opposite (hyperpolarizing) one. © 2015, Springer Science+Business Media New York.
Rodinskii A.G.,Dnipropetrovsk Medical Academy of the Ministry of Public Health of Ukraine |
Serdyuchenko I.Ya.,Dnipropetrovsk Medical Academy of the Ministry of Public Health of Ukraine |
Demchenko T.V.,Dnipropetrovsk Medical Academy of the Ministry of Public Health of Ukraine
Neurophysiology | Year: 2013
In acute experiments on rats, we examined the effects of course systemic introduction of sodium gammahydroxybutyrate (NaGHB, 100 mg/kg, i.p., daily within 3 weeks) on consequences of compression of the right sciatic nerve, SN. In the control group, the nerve was compressed, but NaGHB was not injected. Electrical and force responses of the m. gastrocnemius+soleus (GS) and m. tibialis anterior (TA) evoked by stimulation of the n. tibialis comm. and n. peroneus comm., respectively, at the side of SN impairment and the opposite intact side were recorded. Compression of the SN induced in animals of the control group (with no injections of NaGHB) considerable increases in the values of the threshold and chronaxia of the stimulated nerve, decreases in the amplitude of EMG responses of the muscles, increases in the latencies of these reactions, and also decreases in the force responses developed at single and tetanic isometric contractions of the above muscles. At the side of SN compression, graphs of recovery of the second muscle response under conditions of paired stimulation of the nerves were shifted toward greater interstimulus intervals. Course introduction of NaGHB resulted in more than a twofold increase in the thresholds upon stimulation of the nerves; at the same time, the chronaxia values decreased. The amplitudes of EMG responses of the muscles after NaGHB injections became smaller than in the control, and the latencies of these responses increased. Under these conditions, curves of recovery of the second response at paired stimulation were shifted toward shorter interstimulus intervals. Introduction of NaGHB provided noticeable increases in the force responses of the tested muscles. Such changes were observed bilaterally, and the relative intensities of the corresponding modifications at the side of SN compression and the intact side were close to each other. Possible mechanisms of the effect of NaGHB on the state of the nerve/muscle apparatus of the limb after compression of a large nerve trunk resulting in the development of traumatic neuropathy are discussed. © 2013 Springer Science+Business Media New York.