RESUMO
The role of T-type Ca2+ channels for cardiovascular physiology, in particular blood pressure regulation, is controversial. Selective blockade of T-type Ca2+ channels in resistance arteries has been proposed to explain the effect of the antihypertensive drug mibefradil. In the present study, we used a third generation, time- and tissue-specific conditional knockout model of the L-type Ca2+ channel Cav1.2 (Cav1.2SMAKO mice) to genetically dissect the effects of mibefradil on T- and L-type Ca2+ channels. Myogenic tone and phenylephrine-induced contraction in hindlimb perfusion experiments were sensitive to mibefradil in control mice, whereas the drug showed no effect in Cav1.2-deficient animals. Mean arterial blood pressure in awake, freely moving control mice was reduced by 38+/-2.5 mm Hg at a dose of 1.25 mg/kg bodyweight mibefradil, but not changed in Cav1.2SMAKO mice. These results demonstrate that the effect of the putative T-type Ca2+ channel-selective blocker mibefradil on blood pressure and small vessel myogenic tone is mediated by the Cav1.2 L-type Ca2+ channel.
Assuntos
Anti-Hipertensivos/farmacologia , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio Tipo L/fisiologia , Canais de Cálcio Tipo T/fisiologia , Mibefradil/farmacologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Masculino , Potenciais da Membrana , Camundongos , Camundongos Endogâmicos C57BL , Músculo Liso Vascular/fisiologiaRESUMO
Current knowledge about the molecular mechanisms of NMDA receptor (NMDAR)-independent long-term potentiation (LTP) in the hippocampus and its function for memory formation in the behaving animal is limited. NMDAR-independent LTP in the CA1 region is thought to require activity of postsynaptic L-type voltage-dependent Ca2+ channels (Cav1.x), but the underlying channel isoform remains unknown. We evaluated the function of the Cav1.2 L-type Ca2+ channel for spatial learning, synaptic plasticity, and triggering of learning-associated biochemical processes using a mouse line with an inactivation of the CACNA1C (Cav1.2) gene in the hippocampus and neocortex (Cav1.2(HCKO)). This model shows (1) a selective loss of protein synthesis-dependent NMDAR-independent Schaffer collateral/CA1 late-phase LTP (L-LTP), (2) a severe impairment of hippocampus-dependent spatial memory, and (3) decreased activation of the mitogen-activated protein kinase (MAPK) pathway and reduced cAMP response element (CRE)-dependent transcription in CA1 pyramidal neurons. Our results provide strong evidence for a role of L-type Ca2+ channel-dependent, NMDAR-independent hippocampal L-LTP in the formation of spatial memory in the behaving animal and for a function of the MAPK/CREB (CRE-binding protein) signaling cascade in linking Cav1.2 channel-mediated Ca2+ influx to either process.
Assuntos
Canais de Cálcio Tipo L/fisiologia , Hipocampo/fisiologia , Memória/fisiologia , Plasticidade Neuronal/fisiologia , Receptores de N-Metil-D-Aspartato/fisiologia , Comportamento Espacial/fisiologia , 2-Amino-5-fosfonovalerato/farmacologia , Animais , Anisomicina/farmacologia , Comportamento Animal , Butadienos/farmacologia , Canais de Cálcio Tipo L/deficiência , Relação Dose-Resposta a Droga , Relação Dose-Resposta à Radiação , Interações Medicamentosas , Estimulação Elétrica/métodos , Inibidores Enzimáticos/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Imunofluorescência/métodos , Regulação da Expressão Gênica/efeitos dos fármacos , Hipocampo/citologia , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Potenciais da Membrana/efeitos da radiação , Camundongos , Camundongos Knockout , Proteínas do Tecido Nervoso/efeitos dos fármacos , Proteínas do Tecido Nervoso/fisiologia , Plasticidade Neuronal/efeitos dos fármacos , Plasticidade Neuronal/efeitos da radiação , Nitrilas/farmacologia , Técnicas de Patch-Clamp/métodos , Bloqueadores dos Canais de Potássio/farmacologia , Inibidores da Síntese de Proteínas/farmacologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/fisiologia , Células Piramidais/efeitos da radiação , Tetraetilamônio/farmacologia , Fatores de TempoRESUMO
Calcium influx through voltage gated L-type Ca2+ channels has evolved as one of the most widely used transmembrane signalling mechanisms in eukaryotic organisms. Although pharmacological inhibitors of L-type Ca2+ channels have an important place in medical therapy, the full therapeutic potential of the 4 L-type Ca2+ channel subtypes has not been explored yet. To dissect the physiological relevance of the L-type Ca2+ channel subtype diversity, gene-targeted mouse models carrying deletions of these channels ("knockout mice") have been generated. This review focuses on recent data from studies in mice lacking the Ca(v)1.2 and Ca(v)1.3 pore subunits, which have elucidated some of the roles of L-type Ca2+ channels as mediators of signalling between cell membrane and intracellular processes like blood pressure regulation, smooth muscle contractility, insulin secretion, cardiac development, and learning and memory.
Assuntos
Canais de Cálcio Tipo L/fisiologia , Modelos Animais , Animais , Pressão Sanguínea/fisiologia , Canais de Cálcio Tipo L/genética , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Músculo Liso Vascular/fisiologia , Contração Uterina/fisiologia , Vasoconstrição/fisiologiaRESUMO
Previous neurophysiological studies on prion protein deficient (Prnp(-/-)) mice have revealed a significant reduction of slow afterhyperpolarization currents (sI(AHP)) in hippocampal CA1 pyramidal cells. Here we aim to determine whether loss of PrP(C.) directly affects the potassium channels underlying sI(AHP) or if sI(AHP) is indirectly disturbed by altered intracellular Ca(2+) fluxes. Patch-clamp measurements and confocal Ca(2+) imaging in acute hippocampal slice preparations of Prnp(-/-) mice compared to littermate control mice revealed a reduced Ca(2+) rise in CA1 neurons lacking PrP(C) following a depolarization protocol known to induce sI(AHP). Moreover, we observed a reduced Ca(2+) influx via l-type voltage gated calcium channels (VGCCs). No differences were observed in the protein expression of the pore forming alpha1 subunit of VGCCs Prnp(-/-) mice. Surprisingly, the beta2 subunit, critically involved in the transport of the alpha1 subunit to the plasma membrane, was found to be up-regulated in knock out hippocampal tissue. On mRNA level however, no differences could be detected for the alpha1C, D and beta2-4 subunits. In conclusion our data support the notion that lack of PrP(C.) does not directly affect the potassium channels underlying sI(AHP), but modulates these channels due to its effect on the intracellular free Ca(2+) concentration via a reduced Ca(2+) influx through l-type VGCCs.