Dimebon and tacrine inhibit neurotoxic action of beta-amyloid in culture and block L-type Ca(2+) channels.

Dimebon, a Russian-made drug, inhibited toxic effects of beta -amyloid on cultured neurons. Excessive accumulation of beta-amyloid in the brain is characteristic of Alzheimer dementias. Antialzheimer preparations tacrine and dimebon improve survival of cerebellar granule cells during long-term incubation with Abeta25-35, the neurotoxic fragment of beta-amyloid. Both preparations can block potential-dependent Ca(2+) entry into neurons by about 20%, which is explained by their selective action on L-type Ca(2+) channels. It was assumed that the neuroprotective effect of dimebon and tacrine against Abeta25-35 partially depends on inhibition of potential-dependent Ca(2+) entry.

Thrombin-mediated events implicated in mast cell activation.

It has been suggested that mast cells contain receptors for thrombin because binding of thrombin to peritoneal mast cells (PMCs) results in heparin release. Peritoneal mast cell responsiveness to different thrombin forms was examined by measuring ion conductance, intracellular pH, the concentration of cyclic guanosine monophosphate (cGMP), and release of histamine. Several types of receptors for thrombin are suggested by the results, which demonstrate that: (1) PMCs responded to alpha-thrombin and diisopryopyl-phosphoryl-alpha-thrombin (DIP-alpha-thrombin), but not to gamma-thrombin, by activation of Na/H exchange in reactions involving protein kinase C and by a simultaneous elevation in cell conductance and capacitance; (2) the initial 1-nmol/L alpha-thrombin-induced acidification of PMC cytoplasm was absent in Ca-free medium, and higher doses of alpha-thrombin induced a biphasic reaction (acidification preceeded alkalinization); and (3) PMC stimulation by alpha-thrombin at low concentrations (< 1 nmol/L) resulted in increase of cGMP and simultaneous decrease of histamine release, whereas thrombin concentrations > 1 mumol/L induced the acceleration of histamine release.