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Ca+ Tropomyosin alpha-1 chain Tropomyosin beta chain Beta-1 adrenergic receptor Voltage- depenent L-type calcium channel Voltage- depenent L-type calcium channel Voltage- depenent L-type calcium channel Ryanodine receptor 2 cAMP-dependent protein kinase type I-alpha regulatory subunit Sodium/calcium exchanger 1 Voltage-gated T-type calcium channel (ICaT) Voltage-gated T-type calcium channel (ICaT) Sarcoplasmic/endoplasmic reticulum calcium ATPase 2 cAMP-dependent protein kinase catalytic subunit alpha Acebutolol Ca+ Ca+ Ca+ Na+ Na+ Ca+ Ca+ Ca+ Acebutolol Acebutolol ATP H2O Ca+ ADP Pi Ca+ Ca+ Troponin Troponin G-Protein Signaling Cascade Muscle Contraction Cardiac Myocyte Sarcoplasmic Reticulum Low calcium is unable to bind to troponin to displace tropomyosin from the myosin binding sites on the actin filaments Myosin and actin are unbound allowing the filaments to slide further apart, resulting in muscle relaxation Actin Filament Myosin Filament The beta-1 adrenergic receptor is coupled to and activates the G-protein signalling cascade. Antagonizing the beta-1 receptor blocks this from occurring. The G-protein signalling cascade activates protein kinase which activates calcium channels on the membrane, resulting in calcium influx. Low calcium is unable to activate the ryanodine receptor on the sarcoplasmic reticulum. Time Membrane potential (mV) -40mV (threshold) Pacemaker Action Potential Phase 0- depolarization Phase 3- repolarization Phase 4-spontaneous depolarization With acebutolol Without acebutolol Acebutolol, by antagonizing beta-1 adrenergic receptors, decreases intracellular Ca2+. Phase 4 spontaneous depolarization is Ca2+ dependent, therefore acebutolol decreases the slope of phase 4, increasing the time it takes for threshold to be reached and thus slows heart rate Cytosol Since calcium is linked to activation of muscle contraction. Reducing cytosolic calcium levels reduces muscle contraction Acebutolol enters the bloodstream and once it reaches the heart, it antagonizes the beta-1 adrenergic receptor on the cell membrane of myocytes such that epinephrine stimulation of the heart is reduced. T-tubule Acebutolol is administered as an oral capsule or tablet
Mitochondria Calcium TPM1 TPM2 ADRB1 CACNA1C CACNA2D2 CACNB1 RYR2 PRKAR1A SLC8A1 CACNA1H CACNA1G ATP2A2 PRKACA Acebutolol Calcium Calcium Calcium Sodium Sodium Calcium Calcium Calcium Acebutolol Acebutolol Adenosine triphosphate Water Calcium Adenosine diphosphate Phosphate Calcium Calcium Troponin Troponin G-Protein Signaling Cascade Muscle Contraction
Ca+ TPM1 TPM2 ADRB1 CACNA1C CACNA2D2 CACNB1 RYR2 PRKAR1A SLC8A1 CACNA1H CACNA1G ATP2A2 PRKACA Acebut Ca+ Ca+ Ca+ Na+ Na+ Ca+ Ca+ Ca+ Acebut Acebut ATP H2O Ca+ ADP Pi Ca+ Ca+ Troponi Troponi PW000728 Mus Con Cardiac Myocyte Sarcoplasmic Reticulum Low calcium is unable to bind to troponin to displace tropomyosin from the myosin binding sites on the actin filaments Myosin and actin are unbound allowing the filaments to slide further apart, resulting in muscle relaxation Actin Filament Myosin Filament The beta-1 adrenergic receptor is coupled to and activates the G-protein signalling cascade. Antagonizing the beta-1 receptor blocks this from occurring. The G-protein signalling cascade activates protein kinase which activates calcium channels on the membrane, resulting in calcium influx. Low calcium is unable to activate the ryanodine receptor on the sarcoplasmic reticulum. Time Membrane potential (mV) -40mV (threshold) Pacemaker Action Potential Phase 0- depolarization Phase 3- repolarization Phase 4-spontaneous depolarization With acebutolol Without acebutolol Acebutolol, by antagonizing beta-1 adrenergic receptors, decreases intracellular Ca2+. Phase 4 spontaneous depolarization is Ca2+ dependent, therefore acebutolol decreases the slope of phase 4, increasing the time it takes for threshold to be reached and thus slows heart rate Cytosol Since calcium is linked to activation of muscle contraction. Reducing cytosolic calcium levels reduces muscle contraction Acebutolol enters the bloodstream and once it reaches the heart, it antagonizes the beta-1 adrenergic receptor on the cell membrane of myocytes such that epinephrine stimulation of the heart is reduced. T-tubule Acebutolol is administered as an oral capsule or tablet
Mitochondria Ca2+ TPM1 TPM2 ADRB1 CACNA1C CACNA2D2 CACNB1 RYR2 PRKAR1A SLC8A1 CACNA1H CACNA1G ATP2A2 PRKACA Acebut Ca2+ Ca2+ Ca2+ Na+ Na+ Ca2+ Ca2+ Ca2+ Acebut Acebut ATP H2O Ca2+ ADP Pi Ca2+ Ca2+ Troponi Troponi PW000728 Mus Con