Abstract-Voltage-dependent L-type Ca 2ϩ channels are multisubunit transmembrane proteins, which allow the influx of Ca 2ϩ (I Ca ) essential for normal excitability and excitation-contraction coupling in cardiac myocytes. A variety of different receptors and signaling pathways provide dynamic regulation of I Ca in the intact heart. The present review focuses on recent evidence describing the molecular details of regulation of L-type Ca 2ϩ channels by protein kinase A (PKA) and protein kinase C (PKC) pathways. Multiple G protein-coupled receptors act through cAMP/PKA pathways to regulate L-type channels. ␤-Adrenergic receptor stimulation results in a marked increase in I Ca , which is mediated by a cAMP/PKA pathway. Growing evidence points to an important role of localized signaling complexes involved in the PKA-mediated regulation of I Ca , including A-kinase anchor proteins and binding of phosphatase PP2a to the carboxyl terminus of the ␣ 1C (Ca v 1.2) subunit. Both ␣ 1C and ␤ 2a subunits of the channel are substrates for PKA in vivo. The regulation of L-type Ca 2ϩ channels by Gq-linked receptors and associated PKC activation is complex, with both stimulation and inhibition of I Ca being observed. The amino terminus of the ␣ 1C subunit is critically involved in PKC regulation. Crosstalk between PKA and PKC pathways occurs in the modulation of I Ca . Ultimately, precise regulation of I Ca is needed for normal cardiac function, and alterations in these regulatory pathways may prove important in heart disease. (Circ Res. 2000;87:1095-1102.)Key Words: L-type calcium channel Ⅲ protein kinase C Ⅲ protein kinase A Ⅲ heart Ⅲ regulation Ⅲ phosphorylation T he influx of Ca 2ϩ ions through voltage-dependent L-type Ca 2ϩ channels plays an essential role in cardiac excitability and in coupling excitation to contraction. The depolarizing current through L-type Ca 2ϩ channels (I Ca ) contributes to the plateau phase of the cardiac action potential as well as to pacemaker activity in nodal cells. This influx of Ca 2ϩ triggers the release of intracellular stores of Ca 2ϩ from the sarcoplasmic reticulum, and the ensuing intracellular Ca 2ϩ transient results in activation of the myofilaments. L-type channels can also impact on other cellular processes modulated by intracellular Ca 2ϩ such as gene expression and excitation-secretion coupling. Alterations in density or function of L-type Ca 2ϩ channels have been implicated in a variety of cardiovascular diseases, including atrial fibrillation, 1,2 heart failure, 3-6 and ischemic heart disease. 7 Cardiac L-type Ca 2ϩ channels are regulated by a variety of neurotransmitters, hormones, and cytokines. In fact, the first description of currents carried by this channel revealed its regulation by epinephrine. 8 Sperelakis and Schneider 9 and Reuter and Scholz 10 independently hypothesized that ␤-adrenergic receptor (AR)-mediated stimulation of cardiac L-type Ca 2ϩ channels was due to phosphorylation of the channel by cAMP-dependent protein kinase A (PKA). Extensive electrophysiology experi...

Background: The impact of gut microbiota on the regulation of host physiology has recently garnered considerable attention, particularly in key areas such as the immune system and metabolism. These areas are also crucial for the pathophysiology of and repair after myocardial infarction (MI). However, the role of the gut microbiota in the context of MI remains to be fully elucidated. Methods: To investigate the effects of gut microbiota on cardiac repair after MI, C57BL/6J mice were treated with antibiotics 7 days before MI to deplete mouse gut microbiota. Flow cytometry was applied to examine the changes in immune cell composition in the heart. 16S rDNA sequencing was conducted as a readout for changes in gut microbial composition. Short-chain fatty acid (SCFA) species altered after antibiotic treatment were identified by high-performance liquid chromatography. Fecal reconstitution, transplantation of monocytes, or dietary SCFA or Lactobacillus probiotic supplementation was conducted to evaluate the cardioprotective effects of microbiota on the mice after MI. Results: Antibiotic-treated mice displayed drastic, dose-dependent mortality after MI. We observed an association between the gut microbiota depletion and significant reductions in the proportion of myeloid cells and SCFAs, more specifically acetate, butyrate, and propionate. Infiltration of CX3CR1+ monocytes to the peri-infarct zone after MI was also reduced, suggesting impairment of repair after MI. Accordingly, the physiological status and survival of mice were significantly improved after fecal reconstitution, transplantation of monocytes, or dietary SCFA supplementation. MI was associated with a reorganization of the gut microbial community such as a reduction in Lactobacillus. Supplementing antibiotic-treated mice with a Lactobacillus probiotic before MI restored myeloid cell proportions, yielded cardioprotective effects, and shifted the balance of SCFAs toward propionate. Conclusions: Gut microbiota–derived SCFAs play an important role in maintaining host immune composition and repair capacity after MI. This suggests that manipulation of these elements may provide opportunities to modulate pathological outcome after MI and indeed human health and disease as a whole.

Cardiac fibroblasts (CFs) play critical roles in heart development, homeostasis, and disease. The limited availability of human CFs from native heart impedes investigations of CF biology and their role in disease. Human pluripotent stem cells (hPSCs) provide a highly renewable and genetically defined cell source, but efficient methods to generate CFs from hPSCs have not been described. Here, we show differentiation of hPSCs using sequential modulation of Wnt and FGF signaling to generate second heart field progenitors that efficiently give rise to hPSC-CFs. The hPSC-CFs resemble native heart CFs in cell morphology, proliferation, gene expression, fibroblast marker expression, production of extracellular matrix and myofibroblast transformation induced by TGFβ1 and angiotensin II. Furthermore, hPSC-CFs exhibit a more embryonic phenotype when compared to fetal and adult primary human CFs. Co-culture of hPSC-CFs with hPSC-derived cardiomyocytes distinctly alters the electrophysiological properties of the cardiomyocytes compared to co-culture with dermal fibroblasts. The hPSC-CFs provide a powerful cell source for research, drug discovery, precision medicine, and therapeutic applications in cardiac regeneration.

The structure and function of many cysteine-containing proteins critically depend on the oxidation state of the sulfhydryl groups. In such proteins, selective modification of sulfhydryl groups can be used to probe the relation between structure and function. We examined the effects of sulfhydryloxidizing and -reducing agents on the function of the heterologously expressed pore-forming subunits of the cloned rabbit smooth muscle L-type Ca2+ channel and the human cardiac tetrodotoxin-insensitive Na+ channel. The known sequences of the channels suggest the presence of three or four cysteine residues within the putative pores of Ca2+ or Na+ channels, respectively, as well as multiple other cysteines in regions of unknown function. We determined the effects of sulfhydryl modification on Ca2+ and Na+ channel gating and permeation by using the whole-cell and single-channel variants of the patch-clamp technique. Within 10 minutes of exposure to 2,2'-dithiodipyridine (DTDP, a specific lipophilic oxidizer of sulfhydryl groups), Ca2+ current was reduced compared with the control value, with no significant change in the kinetics and no shift in the current-voltage relations. The effect could be readily reversed by 1,4-dithiothreitol (an agent that reduces disulfide bonds). Similar results were obtained by using the hydrophilic sulfhydryl-oxidizing agent thimerosal. The effects were Ca(2+)-channel specific: DTDP induced no changes in expressed human cardiac Na+ current. Single-channel Ba2+ current recordings revealed a reduction in open probability and mean open time by DTDP but no change in single-channel conductance, implying that the reduction of macroscopic Ca2+ current reflects changes in gating and not permeation. In summary, the pore-forming (alpha 1) subunit of the L-type Ca2+ channel contains functionally important free sulfhydryl groups that modulate gating. These free sulfhydryl groups are accessible from the extracellular side by an aqueous pathway.