Myocytes, CardiacHeart VentriclesAnimals, NewbornMyocardiumVentricular FunctionRats, Sprague-DawleyCardiomegalyCells, CulturedMuscle CellsMyocardial ContractionHeartPhenylephrineCalciumCell SizePatch-Clamp TechniquesRats, WistarCalcium Channels, L-TypeAtrial Natriuretic FactorAction PotentialsConnexin 43Potassium ChannelsHypertrophyProtein Kinase C-epsilonSarcoplasmic ReticulumMembrane PotentialsReceptors, Adrenergic, alpha-1Sodium-Calcium ExchangerSarcomeresSarcolemmaEndothelin-1Protein Kinase CGap JunctionsGuinea PigsCardiotonic AgentsCaffeineIsoproterenolSignal TransductionCalcium SignalingElectrophysiologyEnzyme InhibitorsCalcium ChannelsPhosphorylationAdrenergic beta-AgonistsTime FactorsMitogen-Activated Protein KinasesHeart Conduction SystemAdenoviridaeElectric ConductivityEnzyme ActivationSodiumReceptors, Adrenergic, betaRNA, MessengerSarcoplasmic Reticulum Calcium-Transporting ATPasesRyanodine Receptor Calcium Release ChannelCell SeparationSodium ChannelsBlotting, WesternCalcium-Calmodulin-Dependent Protein KinasesBenzophenanthridinesGene Expression RegulationTransfectionIon Channel GatingPotassiumPhenanthridinesCalcium Channel BlockersDose-Response Relationship, DrugMicroscopy, ConfocalGene ExpressionAnti-Arrhythmia AgentsCalcium Channel AgonistsApoptosisModels, CardiovascularElectric StimulationCalcium-Transporting ATPasesMitochondria, HeartTetracaineFluorescent DyesReceptors, Adrenergic, beta-1Aniline CompoundsXanthenesFormamidesPhosphodiesterase InhibitorsArrhythmias, CardiacRabbitsAdrenergic beta-1 Receptor AgonistsIntracellular FluidAdrenergic alpha-AgonistsRyanodineThapsigarginPotassium Channel BlockersIon TransportElectric Capacitance4-AminopyridineIon ChannelsPotassium Channels, Voltage-GatedAcidosisCaveolin 3Shal Potassium ChannelsSodium-Hydrogen AntiporterKinetics