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Effects of mitogens and other agents on rat mesangial cell proliferation, pH, and Ca2+
M B Ganz1, M C Perfetto, W F Boron
1Renal Division, West Haven Veterans Administration Medical Center, Connecticut 06516.
Abstract:
We investigated effects of various agents on proliferation, intracellular pH (pHi), and intracellular calcium [( Ca2+]i) of rat mesangial cells (MCs) in early passages (2-5). Serum-starved MCs incubated in HCO3- were exposed to one of the following: fetal calf serum (FCS), serotonin, angiotensin II (ANG II), arginine vasopressin (AVP), bombesin (Bom), bradykinin (BK), epidermal growth factor (EGF), epinephrine (Epi), interleukin 1 (IL-1), norepinephrine (NE), neuropeptide Y, oxytocin, substance P (SP), platelet-derived growth factor, or 12-O-tetradecanoylphorbol-13-acetate (TPA). We assessed DNA synthesis from [3H]thymidine uptake during exposure to test agent. All agents except ANG II, NE, Bom, and SP were mitogenic. When MCs were incubated in a HCO3(-) -free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium, maximal mitogenic responses to FCS, AVP, and EGF were 41, 44, and 55% (P less than 0.01) lower, respectively, than those in presence of HCO3-. In absence of HCO3-, agents other than BK and IL-1 produced a biphasic pHi response characterized by a transient acidification followed by a prolonged alkalinization that was both Na(+)-dependent and amiloride-sensitive. In presence of HCO3-, agents produced only a small and gradual acidification, except for IL-1 and Epi. Addition of all agonists except IL-1, EGF, and TPA produced significant transient increases in [Ca2+]i, the magnitudes of which were similar in HCO3- and non-HCO3- buffers. These results demonstrate that, in presence of HCO3-, agents (i.e., NE and ANG II) can produce typical [Ca2+]i transients and still not cause MC proliferation. Conversely, an agent may cause proliferation without eliciting a short-term change in either [Ca2+]i or pHi (i.e., IL-1), a change in [Ca2+]i but not pHi (i.e., Epi), or a change in pHi but not [Ca2+]i (i.e., TPA). Thus, at least for MCs, proliferation in HCO3- can be dissociated from early agonist-induced changes in pHi and [Ca2+]i.
Insights
Rat mesangial cell proliferation is influenced by various agents, with bicarbonate significantly impacting mitogenic responses. Cell proliferation can occur independently of immediate changes in intracellular pH or calcium levels.
Area of Science:
- Cell Biology
- Physiology
- Biochemistry
Background:
- Rat mesangial cells (MCs) play a crucial role in kidney function.
- Understanding the signaling pathways that regulate MC proliferation is essential for kidney research.
- Bicarbonate's role in cellular signaling and proliferation is not fully understood.
Purpose of the Study:
- To investigate the effects of various signaling agents on rat mesangial cell proliferation.
- To examine the influence of bicarbonate on intracellular pH (pHi) and intracellular calcium ([Ca2+]i) responses.
- To determine the relationship between MC proliferation and changes in pHi and [Ca2+]i.
Main Methods:
- Primary rat mesangial cells (passages 2-5) were treated with various agents including FCS, serotonin, ANG II, AVP, EGF, IL-1, and others.
- Cell proliferation was assessed by measuring [3H]thymidine uptake.
- Intracellular pH (pHi) and intracellular calcium ([Ca2+]i) were measured in the presence and absence of bicarbonate.
Main Results:
- Most tested agents were mitogenic for MCs, with bicarbonate significantly enhancing responses to FCS, AVP, and EGF.
- In the absence of bicarbonate, agents induced a biphasic pHi response (acidification followed by alkalinization) that was Na(+)-dependent and amiloride-sensitive.
- Agonist-induced [Ca2+]i transients were largely unaffected by bicarbonate, but proliferation could occur without significant changes in pHi or [Ca2+]i.
Conclusions:
- Bicarbonate plays a significant role in mediating mitogenic responses in rat mesangial cells.
- Agent-induced proliferation in MCs can be dissociated from early changes in intracellular pH and calcium.
- These findings highlight the complex signaling networks regulating mesangial cell growth.