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Spatial and temporal distribution patterns of Na-K-2Cl cotransporter in adult and developing mouse retinas
Baoqin Li1, Kelli McKernan, Wen Shen
1Department of Biomedical Science, Florida Atlantic University, Boca Raton, Florida 33431, USA.
Abstract:
The Na-K-2Cl cotransporter (NKCC) is a Cl(-) uptake transporter that is responsible for maintaining a Cl(-) equilibrium potential positive to the resting potential in neurons. If NKCC is active, GABA and glycine can depolarize neurons. In view of the abundance of GABAergic and glycinergic synapses in retina, we undertook a series of studies using immunocytochemical techniques to determine the distribution of NKCC in retinas of both developing and adult mice. We found NKCC antibody (T4) labeling present in retinas from wild-type mice, but not in NKCC1-deficient mice, suggesting that the NKCC1 subtype is a major Cl(-) uptake transporter in mouse retina. Strong labeling of NKCC1 was present in horizontal cells and rod-bipolar dendrites in adult mice. Interestingly, we also found that a diffuse labeling pattern was present in photoreceptor terminals. However, NKCC1 was barely detectable in the inner retina of adult mice. Using an antibody against K-Cl cotransporter 2 (KCC2), we found that KCC2, a transporter that extrudes Cl(-), was primarily expressed in the inner retina. The expression of NKCC1 in developing mouse retinas was studied from postnatal day (P) 1 to P21, NKCC1 labeling first appeared in the dendrites of horizontal and rod-bipolar cells as early as P7, followed by photoreceptor terminals between P10-P14; with expression gradually increasing concomitantly with the growth of synaptic terminals and dendrites throughout retinal development. In the inner retina, NKCC1 labeling was initially observed in the inner plexiform layer at P1, but labeling diminished after P5. The developmental increase in NKCC expression only occurred in the outer retina. Our results suggest that the distal synapses and synaptogenesis in mouse retinas undergo a unique process with a high intracellular Cl(-) presence due to NKCC1 expression.
Insights
The Na-K-2Cl cotransporter 1 (NKCC1) is crucial for chloride uptake in mouse retinas, particularly in developing outer retinal neurons. Its expression pattern suggests a unique role in distal synapse development and function.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- The Na-K-2Cl cotransporter (NKCC) facilitates chloride uptake in neurons, influencing inhibitory neurotransmission by GABA and glycine.
- Understanding NKCC distribution is vital for comprehending neuronal signaling, especially in the retina where these synapses are abundant.
Purpose of the Study:
- To investigate the distribution and developmental expression of NKCC subtypes in the mouse retina.
- To elucidate the role of NKCC1 in retinal development and its contribution to intracellular chloride levels.
Main Methods:
- Immunocytochemical techniques were employed using antibodies against NKCC1 (T4) and KCC2.
- Retinas from wild-type and NKCC1-deficient mice at various developmental stages (postnatal day 1-21) were analyzed.
Main Results:
- NKCC1 is the predominant subtype in the adult mouse retina, strongly expressed in horizontal cells and rod bipolar cell dendrites.
- NKCC1 expression increases in the outer retina during development, appearing in photoreceptor terminals and horizontal/rod bipolar cells.
- KCC2, a chloride extruder, is mainly found in the inner retina.
Conclusions:
- NKCC1 plays a significant role in chloride homeostasis in the developing mouse retina, particularly in the outer retina.
- The developmental expression pattern of NKCC1 suggests a unique mechanism for synaptogenesis and distal synaptic function involving high intracellular chloride levels.
