Department of Physiology and Biophysics
Joint Appointment with Cardiology
UCD Anschutz Medical Campus
RC1 North Tower, P18-7125
Mail Stop 8307
Aurora, CO 80045
We are interested in the cellular and molecular machinery responsible for cardiac pacemaking and its regulation by the autonomic nervous system.
Automaticity in Sinoatrial Myocytes
Cardiac pacemaking originates within the heart itself: no neural input is required. Instead, each beat of the heart begins as a spontaneous electrical depolarization of specialized pacemaker cells in the sinoatrial node. This property of “automaticity” has fascinated people since prehistory. Yet despite thousands of years of mysticism, medicine, and science, our knowledge of the mechanisms responsible for pacemaking is surprisingly incomplete. One major focus of the lab is to understand the molecular basis for pacemaker activity within individual sinoatrial cells. To this end, we record spontaneous action potentials and membrane currents from isolated sinoatrial myocytes. One current project is to understand the role of hyperpolarization-activated HCN ion channels in pacemaking. Although HCN channels are highly expressed in the sinoatrial node and their blockade slows heart rate, the biophysical mechanisms by which they contribute to spontaneous activity remain obscure.
Figure 1 Spontaneous activity and membrane currents in sinoatrial myocytes.
(A) An isolated mouse sinoatrial myocyte. Note the patch pipette, which appears as a triangular shadow in the lower part of the image. (B) Spontaneous action potentials recorded from a sinoatrial cell. Application of isoproterenol (a β adrenergic agonist) accelerates the firing rate of the single cell by increasing the slope of the “diastolic depolarization” phase of the action potential (arrows). (C) Whole cell HCN channel currents elicited by a voltage step to -120 mV in a single sinoatrial cell in the absence and presence of isoproterenol.
Regulation of pacemaking by the autonomic nervous system
The autonomic nervous system profoundly modulates heart rate by regulating the intrinsic activity of sinoatrial myocytes. In the case of the sympathetic nervous system, this is the classic “fight-or-flight” increase in heart rate. We are interested in the pattern of innervation of sinoatrial myocytes by autonomic neurons, and in the protein complexes and intracellular signaling pathways within sinoatrial myocytes that respond to the autonomic neurotransmitters acetylcholine and norepinephrine. In one current project, we are testing the hypothesis that a macromolecular complex exists at postsynaptic sites where sympathetic neurons contact sinoatrial myocytes. We test this hypothesis using immunocytochemistry and biochemistry.
Regulation of cardiac pacemaking by the autonomic nervous system.
(A) Sympathetic neurons (green) course between myocytes (blue) in a 10 um section from the sinoatrial node. Neurons are visualized with an anti-tyrosine hydroxylase antibody and myocytes are visualized with an anti-myomesin antibody. (B) Partial colocalization (cyan) of a MAGUK scaffolding protein (blue) and HCN4 ion channels (green) in a single sinoatrial cell. Images were collected at the Light Microscopy Facility, housed in the Department of Physiology and Biophysics.
Proenza C and Yellen G (2006) Distinct populations of HCN pacemaker channels produce voltage-dependent and voltage-independent currents. J Gen Physiol, 127(2): 183-190.
Shin K-S*, Maertens C*, Proenza C*, Rothberg BS, and Yellen G (2004) [*equal contributions] Inactivation in HCN channels results from reclosure of the activation gate: Desensitization to voltage. Neuron, 41(5):737-44.
Tran N, Proenza C, Macri VS, Petigara F, Sloan E, Samler S, and Accili EA (2002) A conserved domain in the N-terminus important for assembly and functional expression of pacemaker channels. J Biol Chem., 277(46):43588-92
Macri VS, Proenza C, Agranovich E, Angoli D, and Accili EA (2002) Separable gating mechanisms in a mammalian pacemaker channel.
J Biol Chem., 277(39):35939-46
Proenza, C, Tran N, Angoli D, Zahynacz K, and Accili EA. (2002) Different roles for the cyclic nucleotide binding domain and amino terminus in assembly and expression of HCN channels. J Biol Chem. 277(33): 29634-42
Proenza C, O’Brien JJ, Nakai J, Mukherjee S, Allen PD, and Beam KG. (2002) Identification of a region of RyR1 that participates in allosteric coupling with the a1S (CaV1.1) II-III loop. J Biol Chem. 277(8): 6530-6535
Proenza C, Angoli D, Agranovich E, Macri V, Accili EA. (2002) Pacemaker channels produce an instantaneous current. J Biol Chem. 277(7): 5101-5109.
Stroffekova K, Proenza C, and Beam KG. (2001) The protein-labeling reagent FLASH-EDT2 binds not only to CCXXCC motifs but also non-specifically to endogenous cysteine-rich proteins. Pflugers Arch. 442(6):859-66.
Proenza C, Wilkens CM, Beam KG. (2000) Excitation-contraction coupling is not affected by scrambled sequence in residues 681-690 of the dihydropyridine receptor II-III loop. J Biol Chem. 275(39): 29935-7.
Proenza C, Wilkens C, Lorenzon NM, Beam KG. (2000) A carboxyl-terminal region important for the expression and targeting of the skeletal muscle dihydropyridine receptor. J Biol Chem. 275(30): 23169-74.