Frequency-dependent blockade of T-type Ca2+ current by efonidipine in cardiomyocytes.
ABSTRACT Efonidipine is a dihydropyridine Ca2+ antagonist with inhibitory effects on both L-type and T-type Ca2+ channels and potent bradycardiac activity especially in patients with high heart rate. In the present study, we examined the frequency dependence of efonidipine action on the T-type Ca2+ channel in isolated guinea-pig ventricular myocytes. The potency of efonidipine to inhibit the T-type Ca2+ current was higher under higher stimulation frequencies. The IC50 values were 1.3 x 10(-8), 2.0 x 10(-6) and 6.3 x 10(-6) M under stimulation frequencies of 1, 0.2 and 0.05 Hz, respectively. The reduction of T-type Ca2+ current amplitude was not accompanied by change in the time course of current decay. Efonidipine (10 microM) inhibited T-type Ca2+ current elicited by depolarization from holding potentials ranging from -90 to -30 mV by about 30%; the voltage-dependence of steady-state inactivation was not changed by the drug. Efonidipine slowed the recovery from inactivation following an inactivating prepulse. In conclusion, efonidipine was shown to have frequency-dependent inhibitory effects on the T-type Ca2+ channel, which could be explained by slow dissociation of the drug from the inactivated state of the channel.
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ABSTRACT: Traumatic brain injury (TBI) is a leading cause of death and disability in the United States. Despite more than 30 years of research, no pharmacological agents have been identified that improve neurological function following TBI. However, several lines of research described in this review provide support for further development of voltage gated calcium channel (VGCC) antagonists as potential therapeutic agents. Following TBI, neurons and astrocytes experience a rapid and sometimes enduring increase in intracellular calcium ([Ca2+]i). These fluxes in [Ca2+]i drive not only apoptotic and necrotic cell death, but also can lead to long-term cell dysfunction in surviving cells. In a limited number of in vitro experiments, both L-type and N-type VGCC antagonists successfully reduced calcium loads as well as neuronal and astrocytic cell death following mechanical injury. In rodent models of TBI, administration of VGCC antagonists reduced cell death and improved cognitive function. It is clear that there is a critical need to find effective therapeutics and rational drug delivery strategies for the management and treatment of TBI, and we believe that further investigation of VGCC antagonists should be pursued before ruling out the possibility of successful translation to the clinic.Pharmaceuticals 01/2013; 6(7):788-812.
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ABSTRACT: It has become generally accepted that presynaptic high voltage–activated N-type calcium channels located in the spinal dorsal horn are a validated clinical target for therapeutic interventions associated with severe intractable pain. Low voltage–activated (T-type) calcium channels play a number of critical roles in nervous system function, including controlling thalamocortical bursting behaviours and the generation of spike wave discharges associated with slow wave sleep patterns. There is a growing body of evidence that T-type calcium channels also contribute in several ways to both acute and neuropathic nociceptive behaviours. In the one instance, the Cav3.1 T-type channel isoform likely contributes an anti-nociceptive function in thalamocortical central signalling, possibly through the activation of inhibitory nRT neurons. In another instance, the Cav3.2 T-type calcium channel subtype acts at the level of primary afferents in a strongly pro-nociceptive manner in both acute and neuropathic models. While a number of classes of existing clinical agents non-selectively block T-type calcium channels, there are no subtype-specific drugs yet available. The development of agents selectively targeting peripheral Cav3.2 T-type calcium channels may represent an attractive new avenue for therapeutic intervention. Drug Dev. Res. 67:404–415, 2006. © 2006 Wiley-Liss, Inc.Drug Development Research 03/2006; 67(4):404 - 415. · 0.87 Impact Factor
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ABSTRACT: Grafting of polyacrylamide (PAM) chains was performed onto the backbone of Agar by microwave assisted method, using microwave radiation in synergism with ceric ammonium nitrate (CAN) as the chemical free radical initiator. The intended grafting of the PAM chains were confirmed through intrinsic viscosity study, FTIR spectroscopy and elemental analysis (C, H, N, O & S). Further characterization of the grafted product was done in form of SEM morphology and TGA study. Flocculation efficacy of the synthesized graft copolymers was studied in kaolin suspension, through 'Jar test' procedure. Further, flocculation efficacy of the 'best grade' (as determined by 'jar test' in kaolin suspension) in wastewater was studied for possible application in reduction of pollutant load of wastewater.International journal of biological macromolecules 06/2011; 49(4):591-8. · 2.37 Impact Factor